Augustine of Hippo

Now certainly in the epistle to the Hebrews, when a distinction was to be made between the dispensation of the New Testament and the dispensation of the Old Testament in regard to the fitness of the ages and times, it was written most plainly that not only those visible things but also the word itself were wrought by the mediation of the angels. For it speaks as follows: "To what angel has he ever said, 'Sit at my right hand, till I make your enemies a stool for your feet'? Are they not all ministering spirits, sent forth to serve, for the sake of those who are to obtain salvation?" It is evident from this passage that all those things were not only done by angels but were also done for our sake, that is, for the people of God, to whom the inheritance of eternal life is promised.