Adam Clarke on Luke 22:43

There appeared an angel - from heaven - It was as necessary that the fullest evidence should be given, not only of our Lord's Divinity, but also of his humanity: his miracles sufficiently attested the former; his hunger, weariness, and agony in the garden, as well as his death and burial, were proofs of the latter. As man, he needs the assistance of an angel to support his body, worn down by fatigue and suffering. See at the end of Luk 22:44 (note).