אַךְ־רִ֭יק זִכִּ֣יתִי לְבָבִ֑י וָאֶרְחַ֖ץ בְּנִקָּי֣וֹן כַּפָּֽי׃
내가 내 마음을 정히 하며 내 손을 씻어 무죄하다 한 것이 실로 헛되도다
Rashi
But for nought I cleansed my heart All this refers back to: “And they say, ‘How does God know?’” They also say, “But for nothing and in vain we keep the commandments of the Holy One, blessed be He, for behold, we are plagued all the days.”
Radak
Surely When I served him in vain, I gained nothing in my heart, and in vain did I cleanse myself with cleanliness, meaning my heart is pure and my actions are righteous, yet I am afflicted and not at peace.