History and the Doctrine of Guardian Angels

I stumbled across the following (modern) folk prayer the other day:

May the angels walk beside you always, offering wisdom in times of uncertainty, courage in the face of fear, luck in moments of opportunity, and protection in times of vulnerability.

The prayer is fine as far as it goes, even though I have a tendency to be dismissive of modern folk spirituality: my default response is to look down on such things. The reason for this, I think, is that spirituality is and must be descended from mystical experience, and it is difficult to authenticate the mystical experiences of others; lacking better tools, I favor time as a filter to separate the wheat from the chaff, and so the more archaic the belief, the more likely it is to have had merits worth preserving. However, I realized today that I am being rather unfair to this prayer in particular.

As you all surely know by now, I am very fond of my guardian angel, and so, in an effort to understand them (or as an offering to them, which I suppose is the same thing), I have been tracing the doctrines about these kinds of beings for a while. The earliest source I have found so far is Hesiod, Works and Days ll. 121–6 (tr. Hugh G. Evelyn-White):

αὐτὰρ ἐπεὶ δὴ τοῦτο γένος κατὰ γαῖ᾽ ἐκάλυψε,—
τοὶ μὲν δαίμονες ἁγνοὶ ἐπιχθόνιοι καλέονται
ἐσθλοί, ἀλεξίκακοι, φύλακες θνητῶν ἀνθρώπων,
οἵ ῥα φυλάσσουσίν τε δίκας καὶ σχέτλια ἔργα
ἠέρα ἑσσάμενοι πάντη φοιτῶντες ἐπ᾽ αἶαν,
πλουτοδόται: καὶ τοῦτο γέρας βασιλήιον ἔσχον—,
[...]

But after the earth had covered [the golden] generation—they are called pure spirits dwelling on the earth, and are kindly, delivering from harm, and guardians of mortal men; for they roam everywhere over the earth, clothed in mist and keep watch on judgements and cruel deeds, givers of wealth; for this royal right also they received;— [...]

Translation is treason, and Evelyn-White's is no exception, but as best as I can discern with the help of several dictionaries, Hesiod outlines here the following five tenets:

• Guardian angels live on the earth with us (as contrasted with the gods in heaven, the silver generation in the underworld, etc.).

• Guardian angels are morally good and guide us in right behavior.

• Guardian angels protect us from spiritual harm.

• Guardian angels encourage us through difficult situations.

• Guardian angels dispense good fortune.

Astute readers will note that these five points are the exact same ones from the folk prayer I mentioned above, merely rearranged. One might be inclined to see Providence ensuring continuity of doctrine over the last three thousand years, and if that is so, then it makes for a good antidote to my conservative tendencies.

I suspect Hesiod's teachings go back further still, either to Egypt or Mesopotamia (though I despair of tracing it back any further than that). If anyone knows of textual references from either, I would be grateful.