Gods in other local theolgies had messengers (Zeus had Iris, and later Hermes), probably in imitation of the kings who had messengers to carry their messages everywhere in his domain. People back then didn’t start with their theology de nono, figuring that they had an omnipotent god who could do anything without effort – their gods were constructed in imitation of the political reality threy had. Heaven, after all, wouldn’t be less efficient than their own wonderful government. And their gods wouldn’t lack the offices and features their own rulers had. In fact, they’d have better, souped-up versions. So instead of Zeus communicating directly with the heroes, he had the swiftest or the most beautiful messengers. Or he sent Dreams. The Hebrews were undoubtedly influenced by the same thought processes, and their neighbors, and developed the same things.
After a time, those perfect messengers started to develop their own mythologies and characters. Irisnever really did get much of one, but Hermes did. Likewise, in the earliest writings the angels are a pretty uniform bunch. As time went by, you got specific names and deeds, something the Christians built up a lot – Michael, Raphael, Gabriel, and so on.