"Virtue without prudence is not virtue at all. We should often pray to the Holy Spirit for this grace of prudence. Prudence consists in discretion, rational reflection and courageous resolution. The final decision is always up to us." Source: St. Faustina, Diary: Divine Mercy in My Soul
St. Faustine describes failing greatly when trying to perfect a virtue. Although we should work hard to develop virtue, our progress is dependent on grace. If we do not cooperate with God, we will be frustrated and fail. "When one day I resolved to practice a certain virtue, I lapsed into the vice opposed to [...]
"My child, you cannot always continue in the more fervent desire of virtue, or remain in the higher stage of contemplation, but because of humanity’s sin you must sometimes descend to lower things and bear the burden of this corruptible life, albeit unwillingly and wearily. As long as you wear a mortal body you will [...]
"Which are the foundations of sanctity? We may answer in a single word, Jesus Christ is the model, the grace, and the end. He is the necessary model, in Him we must view the virtues in order to comprehend them. A virtue is but the reproduction of some one of His actions, the imitation of [...]
"The proud man who trusts in himself may well undertake nothing, but the humble man is all the braver that he knows his own helplessness, and his courage waxes in proportion to his low opinion of himself, because all his trust is in God, Who delights to show forth His Power in our weakness, His [...]
"Jesus is the grace, as well as the model, of every virtue: 'Without Me,' He says, 'you can do nothing.' We must, then, be helped by Him. The work of virtue is only a co-operation with the divine action of Jesus Christ in us. He comes to aid us and to make us do what [...]
"Morality did not begin by one man saying to another, 'I will not hit you if you do not hit me'; there is no trace of such a transaction. There is a trace of both men having said, 'We must not hit each other in the holy place.' They gained their morality by guarding their [...]
That all possible kinds of mortification, if they were void of the love of God, could not efface a single sin. Source: Brother Lawrence, The Practice of the Presence of God and The Spiritual Maxims