Midrash su Salmi 130:3

(Exod. 23:21:) PAY HEED TO HIM, AND HEARKEN (SM') TO HIS VOICE. DO NOT REBEL AGAINST HIM, FOR HE WILL NOT PARDON YOUR TRANSGRESSION. You were not worthy of hearing (rt.: SM') my voice. Hearken to (rt.: SM') the voice of an angel. He is unable to pardon your transgressions, because he is from the class who do not sin. Another interpretation (of Exod. 23:21:) FOR HE WILL NOT PARDON YOUR TRANSGRESSION. Why? Because he is an agent (sheliah),⁵⁷Sheliah designates one given power of attorney. It is equivalent to the Gk. term, apostolos (“apostle”), as used by early Christians. and whatever an agent is ordered to do, he does. But I lift up my face to you (i.e., show you favor), as stated (in Numb. 6:26): THE LORD LIFT UP HIS FACE <UNTO YOU>. David said to him: Sovereign of the World, You have delivered me to your angel, one who does not lift up his face. Who can withstand him? (Ps. 130:3) IF YOU, O LORD, {LORD}, KEEP ACCOUNT OF INIQUITIES, WHO WILL WITHSTAND? <Even> if you say there is no forgiveness with you, it is with you, as stated in (vs. 4): FOR WITH YOU THERE IS FORGIVENESS SO THAT YOU MAY BE FEARED.

Another explanation of He will not pardon your transgressions. Why not? For he is only a messenger, and a messenger can only do what he is sent to do. I alone can lift up countenances (i.e., grant pardon), as it is said: The Lord lift up His countenance unto thee (Num. 6:26). David cried out: Master of the Universe, you trust us into the keeping of an angel who cannot pardon us, but if Thou, Lord, shouldest mark iniquities, O Lord, who can stand? (Ps. 130:3). If You should say: Forgiveness is not available to you, For with Thee there is forgiveness that Thou mayest be feared (ibid., 4), therefore do not place over us the angel who is guardian of the Inner Sanctum, since it is said: For he will not pardon your transgressions. Why? For it is said My name is in him (Exod. 23:21) (i.e., he is only my messenger). R. Simeon the son of Lakish said: The name of the Holy One, blessed be He, is coupled with every angel, as it is said: For My name is in him.