Charles Ellicott Commentary Psalms 99:8

"Thou answeredst them, O Jehovah our God: Thou wast a God that forgavest them, Though thou tookest vengeance of their doings." — Psalms 99:8 (ASV)

You took vengeance of their inventions (or, works). —This does not refer to the persons just mentioned but to the people at large. The train of thought is as follows: “There are great saints among us, as in former times, but, as then, their prayers, while often obtaining forgiveness, could not completely avert punishment for sin; so the present community must expect retribution when sinful, in spite of the mediation of the better part of the nation.” The Hebrew style did not favour similes, and hence the poet omits the signs of comparison, and leaves his inference to be drawn by his readers.