Commentary on Matthew 5:43-48
At that time: Jesus said to his disciples: “You have heard that it was said, ‘You shall love your neighbour, and shall hate your enemy.'” And so forth.
But I say to you: “Love your enemies, do good to those who hate you.” Many people, measuring the precepts of God by their own weakness rather than by the strength of his Saints, think it is impossible to perform what they command. They say it is enough if the virtuous do not hate their enemies. To love them is to command more than human nature can bear. We ought to realise that Christ did not command impossible things, although he did command perfect things: David did it to Saul and Absalom; Stephen the Martyr prayed for his enemies who stoned him; Paul wished to be anathema for the sake of his persecutors. This, too, Jesus taught and did when he said: “Father, forgive them, for they know not what they do.”
“Father, forgive them, for they know not what they do.”
That you may be the children of your Father who is in heaven. If observing the commandments of God makes man a son of God, then is man a son of God not from his nature but from his will. “Therefore when you do an almsdeed, sound not a trumpet before you, as the hypocrites do in the synagogues and in the streets that they may be honoured by men.” The man giving an alms and sounding a trumpet is a hypocrite. He who fasts that he may disfigure his face, and that its emaciation may show the emptiness of his stomach – he, too, is a hypocrite. So, too, is he a hypocrite who prays in the synagogues and on the corners of streets, for the sole purpose of being seen by men.
The danger of vain-glory
From all this we may conclude that hypocrites do what they do that they may be glorified by men. It seems to me that, he, too, is a hypocrite who says to his brother, “Let me cast the speck out of your eye,” for he does this through vain-glory, that he may seem just. Wherefore, the Lord says to him: “Hypocrite, first cast out the beam from your own eye.” It is not the act of virtue, but the motive for virtue, which has the reward from God. And if you swerve even but a little from the straight way, it matters not whether you stray to the right or to the left, since you have lost the true way.
– From: St Jerome, Book 1, Commentary on Matthew, Ch. 5-6
(see also: Examination of Conscience, Spiritual Direction, Confession)