St Faustina wrote:
When I went for adoration, I heard these words: My beloved daughter, write down these words, that today My Heart has rested in this convent [the Cracow house]. Tell the world about My mercy and My love.
The flames of mercy are burning me. I desire to pour them out upon human souls. Oh, what pain they cause Me when they do not want to accept them!
My daughter, do whatever is within your power to spread devotion to My mercy. I will make up for what you lack. Tell aching mankind to snuggle close to My merciful Heart, and I will fill it with peace.
Tell [all people], My daughter, that I am Love and Mercy itself. When a soul approaches Me with trust, I fill it with such an abundance of graces that it cannot contain them within itself, but radiates them to other souls. (Diary 1074)