John Calvin Commentary Psalms 143:1

"Hear my prayer, O Jehovah; give ear to my supplications: In thy faithfulness answer me, [and] in thy righteousness." — Psalms 143:1 (ASV)

Hear my prayer, O Jehovah! It is evident that the oppression of his enemies must have been extreme when David laments his case in such earnest and pathetic terms. The introductory words show that the grief he felt was great.

We have shown elsewhere his reason for speaking of God's justice and faithfulness in this connection. Under the term justice, or righteousness, we are not to suppose that he speaks of merit or reward, as some ignorantly imagine, but of that goodness of God which leads him to defend his people. To the same effect, he speaks of God’s truth or faithfulness; for the best proof he can give of his faithfulness is in not forsaking those whom he has promised to help. In helping his people, he shows himself to be a just and true God, both by not frustrating their expectation and insofar as he shows in this extension of mercy what his nature is. For this reason, David very properly encourages himself in prayer by making mention of both.