Knowing God means knowing his steadfast love (covenant faithfulness), justice (right judgment), and righteousness (right behavior, esp. in keeping his promises). See Ex. 34:6–7; Ps. 103:8; Joel 2:12–14; Jonah 3:9–4:2. Paul applied the admonition “let him who boasts boast in the Lord,” based on this text, to the Corinthian Christians (1 Cor. 1:31; 2 Cor. 10:17).
9:23–24 The principle of boasting in God alone is fulfilled in 1 Cor. 1:29–31 (see 2 Cor. 10:17).
ESV Study Bible
9:24 understands and knows Me. Nothing but a true knowledge of God can save the nation. Paul refers to this passage twice (cf. 1Co 1:31; 2Co 10:17).
MacArthur Study Bible
9:24 he has insight, and that he knows me Knowing what Yahweh wants and doing it is the essence of true wisdom and proper worship. Yahweh wants His people to emulate Him in practicing kindness, justice, and righteousness. Israel had fundamentally failed to emulate these aspects of God’s character.
Faithlife Study Bible