4 Therefore does the Lord require this of Peter, “Peter, do you love Me?” As though, “What will you give Me, what will you do for Me, seeing that you love Me?” What was Peter to do for his Lord risen again, and going into heaven, and sitting on the right hand of the Father? As if He had said, “This shall you give Me, this shall you do for Me, if you love Me, feed My sheep; enter in by the Door, not go up by another way.” You heard when the Gospel was being read, “He that enters in by Door, is the shepherd; but he that goes up another way, is a thief and a robber; and he seeks to disperse, and to scatter, and to spoil.” Who is he that enters in by the Door?
He that enters in by Christ. Who is he? He who imitates the Passion of Christ, who acknowledges the Humility of Christ; that whereas God was made Man for us, man may acknowledge himself to be, not God, but man. For whoso wishes to appear God, when he is man, does not imitate Him, who, being God, was made Man. But to you it is not said, Be anything less than you are; but acknowledge what you are. Acknowledge yourself feeble, acknowledge yourself man, acknowledge yourself a sinner; acknowledge that it is He That justifies, acknowledge that you are full of stains.
Let the stain of your heart appear in your confession, and you shall belong to Christ's flock. For the confession of sins invites the physician's healing; as in sickness, he that says, “I am well,” seeks not the physician. Did not the Pharisee and the Publican go up to the temple? The one boasted of his sound estate, the other showed his wounds to the Physician. For the Pharisee said, “I thank You, O God, that I am not as this publican.” He gloried over the other. So then if that publican had been whole, the Pharisee would have grudged it him; for that he would not have had any one over whom to extol himself.
In what state then had he come, who had this envious spirit? Surely he was not whole; and whereas he called himself whole, he went not down cured. But the other casting his eyes down to the ground, and not daring to lift them up unto heaven, smote his breast, saying, “God be merciful to me a sinner.” And what says the Lord? “Verily I say unto you, that the publican went down from the temple justified rather than the Pharisee. For every one that exalts himself shall be abased, and he that humbles himself shall be exalted.” They then who exalt themselves, would go up into the sheepfold by another way; but they who humble themselves, enter in by the Door into the sheepfold.
Therefore said He of the one, “he enters in;” of the other, “he goes up.” He that goes up, you see, who seeks exaltation, does not enter in, but falls. Whereas he that abases himself, that he may enter in by the Door, falls not, but is the shepherd.
Source: Sermons on Selected Lessons of the New Testament (New Advent)