The psalmist concluded with a prayer that God would search him, so it would be clear that he was not like these enemies. Thus he ended this psalm as he began it-with a reference to God"s searching knowledge (cf. Psalm 139:1). David wanted God to test him, as a refiner tests metal, to show that he was loyal to the Lord. Since God knows all, he would know David"s anxious thoughts. He would discover no pain that God"s afflicting him for doing wrong had caused him, or any offensiveness in him that might lead to God"s affliction. Consequently God would preserve his life. [source][source][source]
Knowledge of God"s attributes can bring great peace into the lives of believers. His comprehensive knowledge, personal presence, and absolute power are all working for the welfare of His people. Therefore we should commit ourselves to Him in loyalty and resist those who oppose Him. [source][source][source]