At the end of the 17th century Our Lord appeared to St. Margaret Mary Alocoque (1647-1690) and asked her to spread devotion to His Most Sacred Heart. In a letter written to her Mother Superior in May 1688, St. Margaret Mary set out what is called The Great Promise Our Lord made regarding the Nine First Fridays and what we must do to earn it:

“On Friday during Holy Communion, He said these words to His unworthy slave, if I mistake not: ‘I promise you in the excessive mercy of My Heart that Its all-powerful love will grant to all those who receive Holy Communion on nine first Fridays of consecutive months the grace of final repentance; they will not die under My displeasure or without receiving their sacraments, My divine Heart making Itself their assured refuge at the last moment.'”

First Friday Requirements: To meet the requirements for the First Friday Devotion a person must, on each First Friday for nine consecutive months:

1. Attend Holy Mass
2. Receive Communion
3. Go to Confession*

*Some Catholic resources on this devotion say that Confession is not strictly required unless you need the sacrament in order to receive a worthy Communion, in other words, you need to go to Confession so you can be in the state of grace before you can receive Our Lord in the Blessed Sacrament. Other sources say you must go to Confession with in eight days before or after the Friday. Even if you are in the state of grace. If in doubt, consult your spiritual director. The more prevalent view prescribes the latter

The communicant should have the intention, at least implicitly, of making reparation to the Sacred Heart of Jesus for all the sinfulness and ingratitude of men.

Our Lord made these promises to St. Margaret Mary Alacoque regarding those who practice the Nine First Fridays and have a deep devotion to His Sacred Heart. The Twelve Promises listed below includes the “Great Promise” (number 12).

1. I will give them all of the graces necessary for their state of life. 
2. I will establish peace in their homes. 
3. I will comfort them in all their afflictions. 
4. I will be their strength during life and above all during death. 
5. I will bestow a large blessing upon all their undertakings. 
6. Sinners shall find in My Heart the source and the infinite ocean of mercy. 
7. Tepid souls shall grow fervent. 
8. Fervent souls shall quickly mount to high perfection. 
9. I will bless every place where a picture of my heart shall be set up and honored. 
10. I will give to priests the gift of touching the most hardened hearts. 
11. Those who shall promote this devotion shall have their names written in My Heart, never to be blotted out. 
12. I promise you in the excessive mercy of My Heart that My all-powerful love will grant all to those who communicate on the First Friday in nine consecutive months the grace of final penitence; they shall not die in My disgrace nor without receiving their sacraments; My Divine Heart shall be their safe refuge in this last moment.