Daniel 9:5 - Joseph Benson’s Commentary on the Old and New Testaments

We have sinned, and have committed iniquity Daniel uses the same confession here that is prescribed, in Solomon's consecration prayer, to be used by the Jews in the land of their captivity; with a promise subjoined, of a favourable answer that God would make to their supplications presented to him on such an occasion: see the margin. And being one of the Jewish nation, he speaks of their sins as his own; and, though certainly a most holy man, puts himself among the greatest sinners. There seems to be a kind of gradation in the prophet's confessions here, beginning with sins in general, and rising to rebellion and apostacy.