What does Psalm 26:3 mean?

So far, David has proclaimed his integrity (Psalm 26:1) and asked God to search him, to prove that sincerity (Psalm 26:2). Here, he affirms that he lived with a deliberate focus on God's unfailing love and truth. Of course, David sinned. In at least one case, his sin was severe (Psalm 51). And yet, the long-term course of his life demonstrates faithfulness to the Lord. He loved God and obeyed his Word (Psalm 119:11). He also believed God would keep His covenant promises.

The Christian life includes love for the Lord, which the Holy Spirit puts in the heart at the moment of salvation (Romans 5:5). Having received God's love, we respond to Him by becoming obedient from the heart to His Word (Romans 6:17). Paul describes the profound change which occurs when someone becomes a believer (2 Corinthians 5:17; Ephesians 2:1–5). He credits this to God's great love and grace (Ephesians 2:4–9; Romans 5:8) and cites God's purpose to make believers His workmanship (Ephesians 2:10). A proper response to God's love is a reciprocal love demonstrated in obedience to God. Jesus said, "Whoever has my commandments and keeps them, he it is who loves me" (John 14:21).