כִּֽי־עִמְּךָ֥ הַסְּלִיחָ֑ה לְ֝מַ֗עַן תִּוָּרֵֽא׃
Aber bei dir ist Vergebung, auf dass du gefürchtet werdest.
Rashi on Psalms
For forgiveness is with You You did not give permission to an agent to forgive, as it is said (Exod. 23:21): “for he will not forgive your transgression.”
Rashi on Psalms
in order that You be feared for this, so that no man will rely on the forgiveness of another. (I found this.)