Acts 12:8

‘And the angel said to him, “Gird yourself, and bind on your sandals.” And he did so. And he says to him, “Throw your robe about you, and follow me.”

We must presume that Peter was heavy with sleep, such was the clarity of his conscience, so that the angel had to urgently prod him into action. He bade him to gird himself, that is put his belt on in order to keep his clothing off the ground for fast walking, and bind on his sandals. He wanted Peter to know that he would be coming with him. And Peter did as he was told. Then he urged him to throw his robe around him and follow him.

The detail given suggests that Luke wants us to see Peter as in a daze, and this is brought out in what follows. That the visitant was God-sent is certain, but there is nothing here that necessarily requires that it be a heavenly visitant, apart from the description ‘angel of the Lord' itself. Had it not been for that it could equally have been a messenger of God on earth.