John Calvin Commentary Psalms 119:121

"I have done justice and righteousness: Leave me not to mine oppressors." — Psalms 119:121 (ASV)

I have done judgment and righteousness. The Prophet implores the help of God against the wicked who troubled him, and in doing so, he simultaneously testifies that the harassing treatment he received from them was, on his part, entirely undeserved.

If we wish for God to intervene and help us, it is fitting for us to ensure that we approach Him with the testimony of a good conscience. Since He everywhere promises His aid to the afflicted who are unjustly oppressed, the Prophet's claim is therefore by no means unnecessary. He states that he had not provoked his enemies, but had instead restrained himself from all injury and wrongdoing, and had not even attempted to repay evil with evil.

In asserting that he had at all times done judgment, he means that whatever the wicked practiced, he steadfastly persevered in pursuing integrity and never turned aside from what was just and right in any of his public or private dealings.