Catechism of the Catholic Church
d. Para. 589: . . . "(I)t was most especially by forgiving sins that Jesus placed the religious authorities of Israel on the horns of a dilemma. Were they not entitled to demand in consternation, "Who can forgive sins but God alone?" (Mk 2:7). By forgiving sins Jesus either is blaspheming as a man who made himself God's equal or is speaking the truth, and his person really does make present and reveal God's name (Cf. Jn 5:18; 10:33; 17:6, 26).
Para. 590: Only the divine identity of Jesus' person can justify so absolute a claim as "He who is not with me is against me"; and his saying that there was in him "something greater than Jonah, . . . greater than Solomon," something "greater than the Temple"; his reminder that David had called the Messiah his Lord (Cf. Mk 12:6; 30, 36, 37, 41-42), and his affirmations, "Before Abraham was, I AM"; and even "I and the Father are one" (Jn 8:58;10:30).