I was surprised to notice this morning that the feast of the Guardian Angels--at least as a universal observance--is recent in origin. In 1670 it was assigned to the first free day after Michaelmas (now the feast of the Archangels Michael, Gabriel, and Raphael.)
If you want to believe Pseudo-Dionysius, the guardian angels come from the plain old "angels," as distinguished from the higher orders of Archangels, Principalities, Powers, Virtues, Dominions, Thrones, Cherubim, and finally Seraphim (who are closest to God's throne.)
In my experience much of the talk or preaching we do about angels is pretty confused, and rarely takes seriously their entirely spiritual nature. Nevertheless, this feast day affirms what we say straight away about God in the creed, that he is the Creator of both a seen and an unseen world. This feast reminds us that, contrary to what we might believe if we took all of our religious instruction from the movies, the unseen world is on our side.