I don’t know how much I’d call this “magic,” per se, but the cult of Hermes Trismegistos (or just “Hermetic cult”) is a pretty interesting bit of utter bunk religious history. It’s one of the four schools of gnostic thought I railed about here, but I skipped over it because they’re pretty wacky.

The cult itself is explicitly un-Christian, though it remained active during the formative period of Christianity. Rather than the Christian God, though, they worshiped a god with three aspects, Hermes Trismegistos (Hermes Thrice-Greatest, roughly speaking). Their holy texts are considered by the cult to have been written by HTM before the Biblical flood, and to have been directly passed down from him to them.

Unlike the other gnostic-y schools, though, the cult of HTM was a lifestyle, a spiritual way rather than a philosophical path. Philosophy blended with religion; in addition to “prayer, spiritual offerings, bloodless fraternal meals, and various initiations,” the cult kept with older Egyptian ritual practices—more on this in Meyer’s anthology of Nag Hammadi Scriptures, which is one of the three books I generally recommend to anyone just getting their toes wet in this gnostic stuff. The recently-discovered Hermetic writings (like Discourse on the Eight and the Ninth, which I suggest everyone read for sheer entertainment value) are mostly contained in Nag Hammadi Codex VI, which is the most eclectic of the codices; before that, there was the Corpus Hermeticum, which, as the name suggests, is a collection of Hermetic scriptures.

The interesting bit about the cult of HTM is that just looking at it from a philosophical perspective is not sufficient for understanding it; it’s a blend of philosophy, ritual, and the search for gnōsis, or acquaintance with the deity in question. Unlike the other schools of gnostic thought, Hermetic scriptures represent steps on the way to this knowledge of God/HTM; rather than categorizing the Hermetic writings as “not gnostic” and "gnostic,” we could just as easily call them “realizing God in the material” and “on the way to finding God in the metaphysical.” Hermetic religion, according to Mahé (in the anthology I mentioned above), can be best understood as "an actual religious movement with a deep social impact, based on congregations quite similar to Gnostic communities…[which] accepted popular religion and admired the traditional cults of Egypt.”

If you want to learn more about this particular weird interesting worldview, I’d recommend picking up an introductory text on gnostic thought; Layton’s The Gnostic Scriptures is a standby that’s referenced in most of the other literature, and Jonas’s The Gnostic Religion provides nice overview and critical engagement of sources. More recently, Gérard Vallée published The Shaping of Christianity, which gives not only historical background at an introductory level, but an explanation about the reception of “gnosticism,” both within the general populace and within the proto-orthodox Christian church--and reception's what I gathered you were interested in learning about in the first place, if I'm not entirely mistaken. :)

I hope this helped answer your question; without further clarification, this was the best I could come up with! Cheers!

Edit: A typo.