June 16, 1675, the day of the octave of the Feast of Corpus Christ, the Third apparition of Jesus to St. Margaret Mary Alacoque took place as Margaret Mary was kneeling before the Tabernacle, Our Lord said to her while showing her His Heart:

"Behold the Heart which has so loved men that it has spared nothing, even to exhausting and consuming Itself, in order to testify Its love; and in return, I receive from the greater part only ingratitude, by their irreverence and sacrilege, and by the coldness and contempt they have for Me in this Sacrament of Love. But what I feel most keenly is that it is hearts which are consecrated to Me, that treat Me thus. Therefore, I ask of you that the Friday after the Octave of Corpus Christi be set apart for a special Feast to honor My Heart, by communicating on that day, and making reparation to It by a solemn act, in order to make amends for the indignities which It has received during the time It has been exposed on the altars. I promise you that My Heart shall expand Itself to shed in abundance the influence of Its Divine Love upon those who shall thus honor It, and cause It to be honored."

And in other apparitions:

“My Divine Heart is so impassioned with love for men, that it can no longer contain in itself the flames of its ardent charity, it is necessary that it repay them by its means and that it manifest itself by enriching men with its precious treasures. I disclose to you these treasures; you will see in My Heart the sanctifying and saving graces necessary to restrain the sinners from the abyss of perdition. I have chosen you for the accomplishment of this grand design. The ingratitude of men is more sensible to me than all that I have suffered for them in My Passion. If they will make for me some return of love, I will estimate as little all that I have suffered for them and I would like, if possible, to suffer yet for their advantage.

“I have reserved the devotion to My Sacred Heart for the last centuries so as to gain men by this last gift of My love and to enrich them with the treasures of which My Heart is the source”