Dear friends, the most beautiful feast of the Annunciation is now here, when Our Lady gave Her Heart to God, the Spirit of God overshadowed Her, and the Son of God was Conceived in Her Holy Womb. Let us imitate the perfect consecration Our Lady made of Her Life and Her Will by saying "Fiat" to God. Let us say our own Fiat to God and for Her this day, now almost 2020 years since the day She first said Her Fiat to God for us Her children. As per many sources, Total Consecration to Mary is heavily indulgenced (see for e.g. http://www.brizek.com/mary/tdtmatc.htm and https://www.ecatholic2000.com/montfort/true/devotion.shtml) and at least on particular days, one can receive a plenary indulgence by Total Consecration. On other days, even if not exactly same, there will be similar effects, if we consecrate ourselves without reserve, we can come close to Baptismal innocence. Let us not waste this wondrous festival of the Annunciation, but use it to surrender ourselves wholeheartedly, either for the first time, or renew our consecration, to Jesus and Mary.

Every good work done in grace, especially if it is painful, has a twofold value: a meritorious value that increases the degree of the state of grace in us, and results in a corresponding increase of glory in eternity. And a satisfactory value, that can be used to pay the debts owed to sin. Now, in Total Consecration as St. Montfort explains, we entrust our personal merits to the Blessed Mother only for safe-keeping, merit as such is strictly personal and is not transferred. What is transferred is satisfactory value, applied either to the Souls in Purgatory to pay their debts to Divine Justice, or to dying souls who can be saved by this life offering, or to other souls known to God. 

For a very rough analogy, imagine they are two bank accounts, say there are 1000 credits in the first and 10 credits in the second by all the good works you have done in life, all the Sacraments you have received well etc. The second is what is donated. In return, Our Lady communicates to you Her super-abundant merits so that if you are truly surrendered to Her, you will likely be able not merely to merit much more, but also to obtain much greater satisfaction for sins than before; so, really, if you trust Her totally, and make this act of consecration, or vow for the holy souls, or life offering, in complete faith, blind obedience, and perfect love, you really lose nothing. Nay rather, you will gain very much, both for your soul, for that of your family and loved ones, and all others in the world if you wish. For e.g. your merits will be enhanced very highly to several times what they were, e.g. to 100000 credits or even more, and satisfaction likely will similarly be multiplied several times, say to 10,000. Then, if 1000 souls died with 10 debits remaining, they can all be liberated. The analogy is rough, but the point should be clear - the satisfactory value gained can be used to pay off the debts of others.

"TEXT OF THE LIFE OFFERING
     My dear Jesus, before the Holy Trinity, Our Heavenly Mother, and the whole Heavenly Court, united with your most precious Blood and your sacrifice on Calvary, I hereby offer my whole life to the intention of your Sacred Heart and to the Immaculate Heart of Mary.  Together with my life, I place at your disposal all Holy Masses, all my Holy Communions, all my good deeds, all my sacrifices, and the sufferings of my of my entire life for the adoration and supplication of the Holy Trinity, for unity in our Holy Mother Church, for the Holy Father and priests, for good priestly vocations, and for all souls until the end of the world. 
O my Jesus, please accept my life sacrifice and my offerings and give me your grace that I may persevere obediently until my death.  Amen."
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This life offering must be made with a humble heart, firm resolution, and clear intent.  All prayer, good deeds, suffering, and work done with a pure intention has great merit, if it is offered together with the merits, the sufferings, and the Blood of Jesus Christ. https://marianapostolate.com/life-offering/

This life offering was made known to a saintly Hungarian Nun. The Bishop approved fully and later offered His own life to Our Lady.

The Blessed Mother made Five Great Promises: "THE FIVE PROMISES OF OUR HEAVENLY MOTHER TO THOSE WHO OFFER THEIR LIVES TO HER:
1. Their names will be written in the Hearts of Jesus and Mary, inflamed by love.
2. Their life offering, together with the infinite merits of Jesus, can save many souls from damnation.  All souls who will live until the end of the world will benefit from their life offering.
3. None of their family members will go to hell, even if it seems otherwise, because they will receive, in the depths of their souls, the grace of sincere contrition before the soul departs from their bodies.
4. On the day they offer their lives, their loved ones suffering in Purgatory will be released.
5. I will be with them at the hour of their death.  They will not know Purgatory.  I will carry their souls straight to the presence of the Glorious Trinity, where they will live with me in a special place created by God and will rejoice forever.

See this site for the indulgences earlier attached to the vow for the holy souls: http://www.catholictradition.org/Mary/heroic-act.htm

Souls who make the life offering are recommended to receive Holy Communion frequently and offer them up; at least Spiritual Communion.

There's no private revelation that you don't immediately glom onto, is there?

What are the T&Cs of offering your life? From the way you described it, you just basically say a couple extra prayers and try to live a virtuous life(as we all try to anyway), and suddenly your good works are amplified exponentially and your whole family is saved based off your merits and not theirs. That sounds way too good to be true. Especially since you aren't really "offering your life" when all you're doing is just what you'd be doing anyway. It just sounds like a "Get out of jail free" card in that if you happened to hear about this one prayer from your friend and say it, suddenly getting into Heaven is 10x easier for you and your family just because you said it.