From St. Faustina's Diary, 1488:
Conversation of the Merciful God with a Soul Striving after Perfection
Jesus: I am pleased with your efforts, O soul aspiring for perfection, but why do I see you so often sad and depressed? Tell Me, My child, what is the meaning of this sadness, and what is its cause?
Soul: Lord, the reason for my sadness is that, in spite of my sincere resolutions, I fall again into the same faults. I make resolutions in the morning, but in the evening I see how much I have departed from them.
Jesus: You see, My child, what you are of yourself. The cause of your falls is that you rely too much upon yourself and too little on Me. But let this not sadden you so much. You are dealing with the God of mercy, which your misery cannot exhaust. Remember, I did not allot only a certain number of pardons.
Soul: Yes, I know all that, but great temptations assail me, and various doubts awaken within me and, moreover, everything irritates and discourages me.
Jesus: My child, know that the greatest obstacles to holiness are discouragement and an exaggerated anxiety. These will deprive you of the ability to practice virtue. All temptations united together ought not disturb your interior peace, not even momentarily. Sensitiveness and discouragement are the fruits of self-love. You should not become discouraged, but strive to make My love reign in place of your self-love. Have confidence, My child. Do not lose heart in coming for pardon, for I am always ready to forgive you. As often as you beg for it, you glorify My mercy.
Soul: I understand what is the better thing to do, what pleases You more, but I encounter great obstacles in acting on this understanding.
Jesus:
My child, life on earth is a struggle indeed; a great struggle for My kingdom.
But fear not, because you are not alone. I am always supporting you, so lean on Me as you struggle, fearing nothing. Take the vessel of trust and draw from the fountain of life-for yourself, but also for other souls, especially such as are distrustful of My goodness.
Soul: O Lord, I feel my heart being filled with Your love and the rays of Your mercy and love piercing my soul. I go, Lord, at Your command. I go to conquer souls. Sustained by Your grace, I am ready to follow You, Lord, not only to Tabor, but also to Calvary. I desire to lead souls to the fount of Your mercy so that the splendor of Your mercy may be reflected in all souls, and the home of our Father be filled to overflowing. And when the enemy begins to attack me, I shall take refuge behind the shield of Your mercy. (1488, Diary of St. Faustina)