Michael and Gabriel appear in scripture to deliver a message and leave. Raphael gets a novel.
The book of Tobit stands in the Greek Old Testament, is deuterocanonical for Catholics and Orthodox and outside the Hebrew and Protestant canons. Aramaic and Hebrew fragments of it turned up at Qumran, which settled the long argument about whether the Greek was the original. In it Raphael travels the length of a journey disguised as a kinsman, gives his name as Azarias son of Ananias, and behaves throughout like a companion rather than an apparition. He advises the young Tobias about a fish, and the parts of that fish then drive off the demon Asmodeus and cure the old man's blindness.
Only at the end does he say what he is: one of the seven holy angels who present the prayers of the saints and enter before the glory of the Holy One. That single verse is where the Latin West got its number seven, and the reason lists of archangels so often stop at that figure.
The name is built on the root meaning to heal, and 1 Enoch gives him the healing of the earth itself after the fall of the watchers.
Of all the planetary attributions in this collection, Mercury for Raphael is the one with the strongest independent case. Mercury governs physicians and travellers in the classical planetary characters, and Raphael in Tobit is precisely a physician on a journey. The correspondence looks less like a table and more like a reading.