Question: Did an angel tell Matthew about the temptations of Jesus in the wilderness? Or did Jesus tell the disciples during his ministry?
Answer: There are at least four reasons to think that the answer is the second of the above; that Jesus himself told the disciples the account of the temptations in the wilderness:
(1) if Jesus had not told the disciples then how could they understood his teaching about the devil? This changes our understanding of many verses, such as “Get behind me Satan” (Matthew 16:23 and Mark 8:33). Without knowledge of the 40 day temptation that would sound like Jesus was calling Peter Satan rather than Jesus identifying Peter’s suggestion as tempting.(2) If Jesus had not told the disciples why would an angel tell Matthew one version of the story, while the eye witnesses interviewed by Luke told another version of the story in a different order and with different details. It makes more sense for Jesus to have told the account of the temptations in the wilderness more than once in varying versions, as he did with many of his parables.
(3) If the temptations account had not been part of Jesus’ teaching and had been a secret until revealed to Matthew years later when writing the gospel, this would come as a great shock to Matthew’s readers – and also a great shock to the other disciples. And again Luke’s eye witnesses would not have been able to be interviewed on this point. Luke would also require an angel to tell him if Matthew did. It would also comes as a shock to John who in his gospels records the same three temptations (bread, temple, kingdom) as coming from the Jewish priests and populace, and does not mention the forty days at all.
(4) the narrative has the stamp on it of Jesus himself as author. Who else would be able to say what was in Jesus’ mind and what he went through in the preparation period following his baptism. But it’s more than that. This powerful narrative has the stamp on it not just of a master teacher, but of the Master Teacher. Who else would have been able to teach like this?
There are other reasons for support of this idea. Not least that Satan, the devil, only occurs in allegories and poetry in the Old Testament, but the four points above are already conclusive.
Matthew did not need an angel to provide this account, as the only eyewitness (the Lord Jesus himself) is the original author of the temptation accounts in Matthew 4 and Luke 4. Jesus told it this way.