Thomas Aquinas Commentary Lamentations 3:22-24

"[It is of] Jehovah`s lovingkindnesses that we are not consumed, because his compassions fail not. They are new every morning; great is thy faithfulness. Jehovah is my portion, saith my soul; therefore will I hope in him." — Lamentations 3:22-24 (ASV)

Here he sets forth the experience of divine mercy in the present.

First is the recognition of this: the mercies of the Lord, in that He is not punishing as one who is unmerciful, because He punishes less than what is deserved, not reducing us to nothing. Correct me, O Lord, but with judgment, and not in Your fury, lest You bring me to nothing (Jeremiah 10:24).

Second is the Lord’s approval of this: I, I the Lord, know every morning—that is, clearly. Great is your faithfulness—that is, the faithfulness of Jeremiah, who in the midst of suffering recognizes his blessings. Great is your faith! Let it be done for you as you wish (Matthew 15:28).

Third, he states the intended conclusion: the Lord is my portion, because unlike others who despise Him, I have chosen Him as my portion. The Lord is the portion of my inheritance and of my cup (Psalms 16:5).