Why the Guardian Angel Cannot Pardon Israel's Sins

(Exodus 23:21:) "Be heedful of him and hearken to his voice; do not rebel against him, for he will not pardon your transgression." You did not merit to hearken to My voice, so hearken to the voice of an angel. He is unable to pardon your transgressions, because he is from the company that does not sin. Another interpretation of "for he will not pardon your transgression": Why? Because he is a messenger, and whatever the messenger is commanded to do, he does. But I lift up the face toward you, as it is said (Numbers 6:26): "May the LORD lift up His face <toward you>." David said to Him: Master of the Universe, and to an angel You hand me over—one who does not lift up the face? Who is able to withstand him? "If You, O LORD <my Lord>, should keep account of iniquities, who could stand?" (Psalms 130:3). And should you say that forgiveness is not with You—it is with You, as it is said (Psalms 130:4): "For with You there is forgiveness, that You may be feared."