“Mercy,” said Pope Francis, “is the Lord’s most powerful message.” Speaking without a prepared text, Pope Francis said, “If we are like the Pharisee before the altar, [who said], ‘Thank you, Lord, for not making me like all the other men, and especially not like that fellow at the door, like that publican…,’ well, then we do not know the heart of the Lord, and we shall not ever have the joy of feeling this mercy.” Pope Francis went on to say, “It is not easy to entrust oneself to the mercy of God, because [His mercy] is an unfathomable abyss – but we must do it!” Pope Francis continued, “He has the ability to forget, [which is] special: He forgets [our sins], He kisses you, He embraces you, and He says to you, ‘Neither do I condemn you. Go, and from now, on, sin no more.’ Only that counsel does He give you.” Pope Francis concluded, saying, “We ask for the grace of never tiring of asking pardon, for He never tires of pardoning.”
Notice how our Holy Father used the phrase, 'unfathomable abyss' when referring to Divine Mercy? I'm pretty sure he's quoting St. Faustina and the Chaplet/Novena. There we find the following prayer, suitable for Lent (or any day at 3pm):
You expired, Jesus, but the source of life gushed forth for souls, and the ocean of mercy opened up for the whole world. O Fount of Life, unfathomable Divine Mercy, envelop the whole world and empty Yourself out upon us.
Elsewhere in the Novena, we hear the reference to the abyss of mercy:
Today bring to Me THE SOULS WHO ARE DETAINED IN PURGATORY, and immerse them in the abyss of My mercy. Let the torrents of My Blood cool down their scorching flames. All these souls are greatly loved by Me. They are making retribution to My justice. It is in your power to bring them relief. Draw all the indulgences from the treasury of My Church and offer them on their behalf. Oh, if you only knew the torments they suffer, you would continually offer for them the alms of the spirit and pay off their debt to My justice.