Objection 1. It would seem that one ought not, by humility, to subject oneself to all men. For, as stated above (2, ad 3), humility consists chiefly in man's subjection to God. Now one ought not to offer to a man that which is due to God, as is the case with all acts of religious worship. Therefore, by humility, one ought not to subject oneself to man.
Objection 2. Further, Augustine says (De Nat. et Gratia xxxiv): "Humility should take the part of truth, not of falsehood." Now some men are of the highest rank, who cannot, without falsehood, subject themselves to their inferiors. Therefore one ought not, by humility, to subject oneself to all men.
Objection 3. Further no one ought to do that which conduces to the detriment of another's spiritual welfare. But if a man subject himself to another by humility, this is detrimental to the person to whom he subjects himself; for the latter might wax proud, or despise the other. Hence Augustine says in his Rule (Ep. ccxi): "Lest through excessive humility the superior lose his authority." Therefore a man ought not, by humility, to subject himself to all.
On the contrary, It is written (Philippians 2:3): "In humility, let each esteem others better than themselves."
I answer that, We may consider two things in man, namely that which is God's, and that which is man's. Whatever pertains to defect is man's: but whatever pertains to man's welfare and perfection is God's, according to the saying of Hosea 13:9, "Destruction is thy own, O Israel; thy help is only in Me." Now humility, as stated above (1, ad 5; 2, ad 3), properly regards the reverence whereby man is subject to God. Wherefore every man, in respect of that which is his own, ought to subject himself to every neighbor, in respect of that which the latter has of God's: but humility does not require a man to subject what he has of God's to that which may seem to be God's in another. For those who have a share of God's gifts know that they have them, according to 1 Corinthians 2:12: "That we may know the things that are given us from God." Wherefore without prejudice to humility they may set the gifts they have received from God above those that others appear to have received from Him; thus the Apostle says (Ephesians 3:5): "(The mystery of Christ) was not known to the sons of men as it is now revealed to His holy apostles." On like manner. humility does not require a man to subject that which he has of his own to that which his neighbor has of man's: otherwise each one would have to esteem himself a greater sinner than anyone else: whereas the Apostle says without prejudice to humility (Galatians 2:15): "We by nature are Jews, and not of the Gentiles, sinners." Nevertheless a man may esteem his neighbor to have some good which he lacks himself, or himself to have some evil which another has not: by reason of which, he may subject himself to him with humility.
Reply to Objection 1. We must not only revere God in Himself, but also that which is His in each one, although not with the same measure of reverence as we revere God. Wherefore we should subject ourselves with humility to all our neighbors for God's sake, according to 1 Peter 2:13, "Be ye subject... to every human creature for God's sake"; but to God alone do we owe the worship of latria.
Reply to Objection 2. If we set what our neighbor has of God's above that which we have of our own, we cannot incur falsehood. Wherefore a gloss [St. Augustine, QQ. lxxxiii, qu. 71 on Philippians 2:3, "Esteem others better than themselves," says: "We must not esteem by pretending to esteem; but we should in truth think it possible for another person to have something that is hidden to us and whereby he is better than we are, although our own good whereby we are apparently better than he, be not hidden."
Reply to Objection 3. Humility, like other virtues, resides chiefly inwardly in the soul. Consequently a man, by an inward act of the soul, may subject himself to another, without giving the other man an occasion of detriment to his spiritual welfare. This is what Augustine means in his Rule (Ep. ccxi): "With fear, the superior should prostrate himself at your feet in the sight of God." On the other hand, due moderation must be observed in the outward acts of humility even as of other virtues, lest they conduce to the detriment of others. If, however, a man does as he ought, and others take therefrom an occasion of sin, this is not imputed to the man who acts with humility; since he does not give scandal, although others take it.
Source: Summa Theologica (New Advent)