From a sermon of St. Augustine:

“The Pharisee could at least have said: I am not as many men. Hwat does as the rest of men mean, other than everyone except himself? I, he says, am just, all the rest are sinners. I am not as the rest of men, unjust, extortioners, adulterers. And at that very moment, you take occasion for greater pride from your neighbor, the publican. As that publican, he says. I am unique, he thinks in his heart; he belongs to the crowd. I am not such as he is, for through my righteous acts I have proven that I am not unrighteous.

I fast twice a week, I pay tithes on all that I possess. Try to find in his talk something he requests from God; you will discover nothing. He went up to pray ? Certainly not to ask God for help, but to praise himself. Not to petition God owuld not have been so bad, but to praise himself and moreover to mock another who did! But the publican stood afar off, but the Lord considered him very near. For the Lord is enthroned on high, but looks kindly upon the lowly. The highbrows such as that Pharisee, He recognizes from afar. Yes, God knows such from afar, but He does not pardon them.

“Note now the publican’s humility. Is it a negligible point that he stood afar off? Or that he did not lift up his eyes to heaven? He did not look so that he could be looked upon. He did not dare to gaze upwards; although his conscience pressed him down, hope buoyed him up. Read further. He kept striking his breast. He would punish himself, and, therefore, the Lord took pity on him. He kept striking his breast saying: Lord, be merciful to me a sinner. Now you see who it is that prays. Why are you surprised when God forgives after he confesses?”

From The Church’s Year of Grace, Vol. 4 by Dr. Pius Parsch. The Liturgical Press, 1959.