Catena Aurea on Matthew 28:1–7: Augustine of Hippo

It may disquiet some, how it is that according to Matthew though the Angel sate upon the stone after it had been rolled back from the sepulchre, whereas Mark says that the women having gone into the sepulchre, saw a young man sitting on the right hand. Either we may suppose that they saw two, and that Matthew has not mentioned him whom they saw within, nor Mark him whom they saw without the sepulchre; but that they heard from each severally what the Angels said concerning Jesus.

Or the words, “entering into the sepulchre,” [Mark 16:5] may mean entering into some enclosed place, which probably there might be in front of the rock out of which the sepulchre was hewn; and thus it might be the same Angel whom they saw sitting on the right hand, whom Matthew describes as sitting on the stone which he had rolled back.