For the Pharisee to fast twice a week (v. 12) was more than is required by any biblical standard. By exalting his own works, the Pharisee revealed that his entire hope lay in his not being as bad as someone else. He utterly lacked any sense of his own unworthiness and sin.
The tax collector’s humility is notable in everything about his posture and behavior (v. 13). Here was a man who had been made to face the reality of his own sin, and his only response was abject humility and repentance. He contrasts with the Pharisee in virtually every detail. “God, be merciful to me a sinner!” He had no hope but the mercy of God. This is the point to which the law aims to bring every sinner (see Rom. 3:19, 20; 7:13; Gal 3:22–24). He was “justified” (v. 14), i.e., reckoned righteous before God by means of an imputed righteousness.