Additional proof of the incompatibility of sin and sonship; the very object of Christ’s manifestation in the flesh was to take away (by one act, and entirely, aorist) all sins, as the scapegoat did typically.
and - another proof of the same.
in him is no sin - not “was,” but “is,” as in 1Jo 3:7, “He is righteous,” and 1Jo 3:3, “He is pure.” Therefore we are to be so.