What are the requirements of the First Friday devotion and what did Christ promise to those who fulfill it?
I need nothing but God, and to lose myself in the heart of Jesus." St. Margaret Mary Alacoque
Beginning on December 27, 1673 and continuing for another 18 months, St. Margaret Mary Alacoque (1647-1690) received several visions of Our Lord in which He revealed the profound depths of His Sacred Heart:
And He showed me that it was His great desire of being loved by men and of withdrawing them from the path of ruin that made Him form the design of manifesting His Heart to men, with all the treasures of love, of mercy, of grace, of sanctification and salvation which it contains, in order that those who desire to render Him and procure Him all the honor and love possible, might themselves be abundantly enriched with those divine treasures of which His heart is the source." Revelations of Our Lord to St. Mary Margaret Alacoque
What are these "divine treasures" of Christ that St. Margaret Mary speaks of? They are commonly called "the 12 promises of the Sacred Heart of Jesus":
I will give them all of the graces necessary for their state of life.
I will establish peace in their houses.
I will comfort them in all their afflictions.
I will be their strength during life and above all during death.
I will bestow a large blessing upon all their undertakings.
Sinners shall find in My Heart the source and the infinite ocean of mercy.
Tepid souls shall grow fervent.
Fervent souls shall quickly mount to high perfection.
I will bless every place where a picture of my heart shall be set up and honored.
I will give to priests the gift of touching the most hardened hearts.
Those who shall promote this devotion shall have their names written in My Heart, never to be blotted out.
I promise you in the excessive mercy of My Heart that My all-powerful love will grant to all 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.
To obtain these promises, you simply need to attend Mass and receive Communion for nine consecutive first Fridays (of each month).