Jesus said to St. Faustina many things.
Allow me to quote from her diary, which has been approved by the Church:
"Tell souls that from this fount of mercy [referring to Confession] souls draw graces solely with the vessel of trust. If their trust is great, there is no limit to My generosity. The torrents of grace inundate humble souls. The proud remain always in poverty and misery, because My grace turns away from them to humble souls."
"Oh, how much I am hurt by a soul's distrust! Such a soul professes that I am Holy and Just, but does not believe that I am Mercy and does not trust in My Goodness. Even the devils glorify My Justice but do not believe in My Goodness."
"When a soul praises My goodness, Satan trembles before it and flees to the very bottom of hell."
"Satan can even clothe himself in a cloak of humility, but he does not know how to wear the cloak of obedience and thus his evil designs will be disclosed."
"Satan has admitted to me[Faustina] that I am the object of his hatred. He said that "a thousand souls do me less harm than you do when you speak of the great mercy of the Almighty One. The greatest sinners regain confidence and return to God , and I lose everything. But what is more, you persecute me personally with that unfathomable mercy of the Almighty One." I took note of the great hatred Satan has for the mercy of God. He does not want to acknowledge that God is good."
"Today the Lord said to me, I have opened My Heart as a living fountain of mercy. Let [souls] approach this sea of mercy with great trust. Sinners will attain justification, and the just will be confirmed in good. Whoever places his trust in My mercy will be filled with My divine peace at the hour of death."
"Tell them that no soul that has called upon My mercy has been disappointed or brought to shame. I delight particularly in a soul which has placed its trust in My goodness. "
"The graces of My mercy are drawn by means of one vessel only, and that is - trust. The more a soul trusts, the more it will receive. Souls that trust boundlessly are a great comfort to Me, because I pour all the treasures of My graces into them. I rejoice that they ask for much, because it is My desire to give much, very much. On the other hand, I am sad when souls ask for little, when they narrow their hearts."
"This evening, Jesus said to me, My daughter, do you need anything? I answered, "O my Love, when I have You I have everything." And the Lord answered, If souls would put themselves completely in My care, I Myself would undertake the task of sanctifying them, and I would lavish even greater graces on them. There are souls who thwart My efforts, but I have not given up on them; as often as they turn to Me, I hurry to their aid, shielding them with My mercy, and I give them the first place in My compassionate Heart."
"Entrust everything to Me and do nothing on your own, and you will always have great freedom of spirit. No circuмstances of events will be able to upset you."
"heaven and earth would pass away before My Mercy didn't embrace a soul that trusted in It."