51 But I contend not with those, who assert that a man can in this life live without any sin: I contend not, I gainsay not. For perhaps we take measure of the great from out our own misery, and, comparing ourselves with ourselves, understand not. One thing I know, that those great ones, such as we are not, such as we have not as yet made proof of, by how much they are great, by so much humble themselves in all things, that they may find grace before God. For, let them be how great soever they will, “there is no servant greater than his Lord, nor disciple greater than his master.” And assuredly He is the Lord, Who says, “All things have been delivered unto Me of My Father;” and He is the Master, Who says, “Come unto Me, all you who labor, and learn of Me;” and yet what learn we? “In that I am meek,” says He, “and lowly of heart.”
Source: On Holy Virginity (New Advent)