As Peter Herbeck reminded us back in 2016, 'Did you know that the Church has an infinite capacity for regeneration? Did you know that? Did you know that the Church has right now all the power, every resource it needs, to conquer every enemy strategy the enemy brings against Her.' And it is precisely when the Church is looking the deadest and most bedraggled that we can expect the resurrection power of Jesus to come upon Her.
There are heightened expectations at the moment for something like this to begin before the end of 2019, with Brexit when it actually happens, as some form of a catalyst.
Consider:
https://lanavawser.com/2019/10/30/i-heard-the-lord-say-the-last-few-months-of-2019-are-going-to-be-explosive/
and https://www.openheaven.com/2018/07/10/three-waves-of-a-coming-baby-boom-and-strategies-for-preparation-by-christy-johnston/
Now for the chicken and the egg paradox: Are we in the 'if and when it happens we will deal with it then' camp or are we in the 'is some of this dependent on us being like Noah and taking God at His word and doing some practical stuff in preparation' camp? Is our lack of preparation part of the delay problem?
Consider the following scenario: an act of God causes 1000 consciences to awaken and they all rush to your church community to get themselves right with God. What do you do?
And what if it is 10,000 people? That's a lot of people who will expect us to know what to do to help them all.
When the active presence of God manifests itself in a place, people have life-changing encounters with God, and no one, but no one, wants to leave a place that is experiencing divine visitation. So expecting people to go down the shops to get supplies just isn't going to work, you need to have the supplies stockpiled already. Call it 'The Noah Storeroom' or the 'When God Shows Up Cache' or similar, expect to get laughed at like Noah was, but do it anyway. Also think long term, God is wanting to add these people to your community permanently. There is also no guarantee that you won't be overwhelmed by God and unable to function as a leader, marshal or administrator, so talk to your teams and make them aware of what your strategy is for when the Flood of Grace comes. Ask God what that strategy should be.
So here are some thoughts, just looking at things from a practical perspective and a decidedly Catholic one because we need to do more preparation than anyone else.
The number one thing people will want is the sacrament of penance, and lengthy confessions. There might be a humungous crowd, but they each need to hear the blessed words of absolution personally. While they wait for their turn they are going to need some refresher teaching on how the sacrament works, how to prepare, what to confess, why the given penance is important etc. Many of them will be in a blubbering mess, before, during and after they get into the confessional.
A practical thing to do is for dioceses and parishes to audit how many non-active priests are within their diocesan and parish boundaries, get in contact with them, and have them on some kind of group alert system. They may be retired, if so, keep in regular contact with them. They may have been laicised for various reasons, but in emergencies, and this would qualify for an emergency, they can exercise priestly faculties. You are going to need them hearing confessions. If you are a bishop, then you should start working out what needs to be done canonically now to get laicised priests as sacramentally active as possible, as quickly as possible, in such a scenario.
The best people to do the refresher teaching on the sacrament of penance will be those who are already on the parish sacramental preparation teams. Parish priests should talk with the parish sacramental preparation co-ordinator about how to handle such a scenario. They would already have some experience in ushering primary school children for their first confessions.
Do you have brochures for people returning to the sacrament of penance after a long absence? Start looking for good examples of them online, or get new ones written. Have them ready to print. Put all the links and files you need in a special folder on your computer, so that you can quickly find them all in one place. Have a back-up paper version in your filing cabinet.
Begin a stockpile of tissues, a stockpile of scripture booklets (like the ones they provide for World Youth Day pilgrims, with a Gospel, another book from the Bible and a Psalm or two) and a stockpile of toilet paper.
Talk to your parish team about setting up triage protocols, because you are going to need to quickly ascertain who has never been baptised, who can't remember if they were baptised, those baptised under other traditions, lapsed Catholics, fringe Catholics and committed Catholics. Baptism (and conditional Baptism), could reduce the strain on the confessionals, but you will need a diocesan approved video presentation on what living out the Nicene Creed means as a minimum preparation for the baptism of those who have reached the age of reason and beyond.
Purchase additional baptismal registers and baptismal certificates at both parish and diocesan levels.
Space is going to be at a premium, so as quickly as possible, get all the cars out of the parish car parks and make them pedestrian access only. You could have several groups learning from different group leaders across the car park - weather permitting.
People are going to want Jesus. Setting up a monstrance with a consecrated host in the church will help with that. If you have a spare or secondary monstrance, set up an additional adoration space in the parish hall as well. You may need to set up wardens or guards from the ranks of acolytes and senior altar servers around those monstrances to keep order. People under the influence of religious zeal have been known to do some mighty crazy things, especially if that zeal is coupled with ignorance.
People are going to need to learn how to pray. Having an area set aside with a Marian shrine/statue and a continuous Rosary being prayed with scripture meditations prior to each decade mystery will help. Stockpile inexpensive sets of rosary beads.
If the repentance is Holy Spirit genuine, then practical steps to change lives will be needed. Wherever you normally have the paschal fire for the Easter Vigil can be the place people can bring unholy objects to have them burned, bad magazines, bad books, crystals, occult items etc.
People in non-married relationships may come under the conviction of the Holy Spirit to get married. You will need teams of people to listen to them, to ascertain if they are free to enter into sacramental marriage, and then organise groups of couples for marriage ceremonies and renewal of vow ceremonies.
Purchase additional marriage registers and marriage certificates, at both parish and diocesan levels.
Under a move of God of such a magnitude, people are going to start manifesting the charismatic gifts of the Holy Spirit. Make sure you have literature and links on hand for them to be able to begin to understand what the Holy Spirit is doing in them, and how to co-operate with it. You are going to need protocols for how to discern and release prophetic words.
Some people may also manifest demonic influence. To deal with that, the diocesan bishop should have a plan in place. He is the chief exorcist of the diocese, and should have already appointed other exorcists. Training should begin now to enable more priestly exorcists to be appointed, and for all diocesan priests to be trained in what they are already authorised to do in such circumstances, and in what must be referred to those with specialist training.
Once the Holy Spirit activates hearts in repentance, then they will experience a hunger for catechesis. Start researching now to discover what good programmes are out there, and purchase or subscribe to them. Then when God's grace hits, get a quality video series set up for viewing in a large meeting room with automatic repeat.
Mobilise those who have been on team for RCIA (Rite of Christian Initiation of Adults) to be the 'go to' people for those that have specific theological questions or hurdles that they need to overcome in order to take the next step on their journey of faith.
You will need printed and laminated lists of good books for people to download on their mobile phones and similar devices on topics such as prayer, sacraments, catechism, charisms, scripture, conversion testimonies that are highly recommended. The last thing you want is for people hungry for catechesis to find online teaching resources that contain doctrinal errors.
It is our duty to help people get to the best sources of teaching quickly. Many people have mobile phones with internet capability, help them use that technology to help them get the recommended teaching that they need.
People on fire with the Holy Spirit are going to want to be active in evangelisation, immediately. Remind them that even St Paul went off to pray, fast and study first. Work out in advance a way to get them into teams to do the necessary preparation, preferably each with an experienced evangelist as a leader, and then send them out in teams. Each sent out team should return together for debriefing, further teaching based on their experiences, and prayer for those they reached out to.
Real repentance will want to express itself in acts of penance, viz prayer, fasting, almsgiving, service to the poor. It will be far better to give people direction on how to respond to this call to penance and reparation, than to leave them without guidance. Think now about how best such holy responses could be channelled to the greatest good, and pray for divine wisdom as you work on that. Consider where the greatest needs in your community are, and which local service organisations are the best ones with track records of integrity and effectiveness. Some people will want to go beyond what prudence suggests, and they will need to be helped so that they bank that fire a bit so as to become sustainable rather than flaming out quickly.
People are going to need to tell their stories about how God's grace rescued them. So you will need teams of listeners and recorders. The better stories should be publicly told, as ongoing encouragement to the church community and in praise to God. Discernment will be needed for who, when, and how such stories are to be released, and whether his/her conversion has deepened enough for it to withstand notoriety.
When such moves of God happen, it can get very chaotic and messy in a good way. The more we can help people ground the profound God experiences they have had in daily prayer, reading of scripture, and frequent recourse to the sacraments, and in the accountability of regular sharing of experiences in small to medium groups, the more fruitful and lasting that grace will be within them. But it takes all hands on deck to steward extraordinary moves of the Holy Spirit like this, far more than just the priest and a handful of helpers. Training up people now who could be effective leaders of small to medium groups would be very prudent.
Many ministry teams will need to go on 24/7 rostering initially, in shifts, especially the music ministry teams. Whatever normal was will have to be suspended for a while until a new normal settles.
The chances of big increases in people asking questions about the validity of past marriages are significant. Beginning to train extra people for the diocesan marriage tribunals would be a wise thing to do.
What needs to be prevented is a decision making bottle-neck focused on the person of the parish priest. Start thinking carefully about what decisions can be devolved to trusted people in senior parish leadership positions and which decisions absolutely must go to the parish priest, and what kind of communication structures would facilitate that. For common requests maybe a pre-prepared checklist of requirements for approval could be very useful.
The more preparation gets done, the fewer people will dissipate the extraordinary grace and slip through the cracks unchanged and without being incorporated into the parish community of faith and into the mission of Jesus.
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I will add to this when I can, especially useful links and file downloads.
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Examples of small booklets of scripture:
Three versions suitable for Sacrament of Penance
4 per A4 page

actcontrition_pdf.pdf |
6 per A4 page

prayerforagoodconfession_pdf.pdf |
With a crowd of people hungry for God, helping them learn to pray by learning to pray the Rosary and meditate on the various scenes in the life of Jesus is a good idea. This is also good as an inexpensive follow-up, for how to pray the Rosary at home.
Double sided, tri-fold A4 page

rosarycrusadew10_pdf.pdf |
This is a good prayer to lead people into a re-commitment to God with, or to recommend as a follow-up daily prayer for anyone who has just had a life changing encounter with God.
4 per A4 page

miracleprayerw10_pdf.pdf |
includes simple examination of conscience
Double-sided, tri-fold A4 page

penancew10_pdf.pdf |
includes excerpts from the diary of St Faustina
about how much God wants us to come and receive His mercy.
Double-sided, tri-fold A4 page

mymercyisforyouw10_pdf.pdf |
Including most of the prayers required to pray the Rosary,
and other prayers that Catholics assume everyone knows 'off-by-heart'. i.e. this is a cheat sheet to help new converts and reverts get up to speed.
Single-sided A4 page

commonprayers_pdf.pdf |
True conversion is accompanied by a desire to reparate for sin, and praying the Stations of the Cross (any version) is useful as a start for satisfying that desire.
Double-sided, tri-fold A4 page

stationspassionistw10pdf.pdf |
In this version, Jesus talks to us as 'His other self' and encourages us to see how we can be united to His Passion in the regular events of every day life.
Double-sided, tri-fold A4 page

stations2w7everymanpdf.pdf |
If there has been a major movement of God, then the natural consequence is people receiving charisms of healing, prophecy, words of knowledge, discernment, speaking in tongues, deliverance etc. Chances are you will have significant numbers of people needing help to understand what God is doing in them and through them, and what is OK and what is not OK. This document which distills 50 years of wisdom from the Catholic Charismatic Renewal will help you get lots of people 'on the same page' quickly, and it will also reassure them that what they are experiencing is normal for the Holy Spirit.
If you haven't read it yet, read it now, so that you are familiar with the contents. That way you will be able to point specific people to the specific parts of the content that they need - when the time comes.
32 x A4 pages

iccrs_charismschool_melbourne_march2019_final_pdf.pdf |
This is the shortest of the Gospels, and is particularly useful for helping people come to a decision about who Jesus is.
At the link below you will find a simple 16 week Bible Study of this Gospel with discussion starters.
Resources - Study Group