The idea of guardian spirits or angels was fairly widely known throughout the West during the period of antiquity, though these took many different forms.
For example, the Romans worshipped spirits called the lares, who were ancestor spirits who remained to guard over a family and household. This entailed protection from harm as well as protection of the family’s hearth and bounty. The Romans also believed in spirits called genii (sg. genius), who were associated with a particular person, place, or concept, and charged with guarding and protecting the virtue of that which they watched over. The office of Roman emperor had a genius, as did the entire people of the Roman Empire.
Roman subjects paid a kind of spiritual tax in the requirement to regularly offer a small sacrifice, usually a small pastry or cake, to the genii of the emperor and the Roman Empire. Jews were exempted from making this sacrifice by special treaty, but that dispensation did not apply to Christians. Refusing to make this sacrifice was the most frequent act for which Christians were condemned during the waves of persecution that sometimes swept through the Empire.
Among the various sects of Judaism, the idea of protective spirits was adopted gradually, though naturally as angels. Daniel, when sent to the lions’ den, was protected by an angel, though it does not read as if this was an angel permanently appointed to protect him. In the Book of Enoch are mentioned angels sent to guard over the righteous (and, according to the Epistle of Jude, to execute the Lord’s judgment). Also, the Book of Enoch describes several archangels whose duties include promotion of justice, especially Michael.
It is this type of guardian angel who appears in Acts 12, in which an angel freed Peter from jail. When Peter made his way to the house of Mary the mother of John, he knocked at the gate, only to have the apostles think, since it can’t be him (he’s in prison!) maybe it’s his angel.
The Holy Spirit, as a guide and protector to the body of the church, plays a role not unlike the genius of the Empire. This is also analogous to the Kabbalistic idea of the Keneset Yisrael, the soul of the body of Israel – a spiritual bond connecting the members of the nation together as one body.
The Gnostics also spoke about guardian angels, but their understanding was somewhat different. An excellent essay, “Joined to an Angel,” describes the role of the guardian angel in the Valentinian scripture and its importance in the Gnostic sacraments – especially the Sacrament of the Bridal Chamber, which was not a marital ceremony between man and woman, but a marriage between the aspirant and their guardian angel, spiritually analogous to the marriage of Christ and Sophia.
In the Valentinian tradition, each person has an angel who is a go-between between them and the divine presence — but the connection is even deeper than that. The Gospel of Philip describes the union with the guardian angel by way of an analogy:
The forms of evil spirit include male ones and female ones. The males are they which unite with the souls which inhabit a female form, but the females are they which are mingled with those in a male form… And none shall be able to escape them, since they detain him if he does not receive a male power or a female power, the bridegroom and the bride. One receives them from the mirrored bridal chamber. When the wanton women see a male sitting alone, they leap down on him and play with him and defile him. So also the lecherous men, when they see a beautiful woman sitting alone, they persuade her and compel her, wishing to defile her. But if they see the man and his wife sitting beside one another, the female cannot come into the man, nor can the male come into the woman. So if the image and the angel are united with one another, neither can any venture to go into the man or the woman.
The image (eidolon) is a Gnostic term for the material body, and the implication is that the angel is almost like another half of your soul without whom you are incomplete.
This esoteric notion of the guardian angel has its roots (as do many of the Gnostic ideas) in the writings of Plato. During the classical period, the Greek words for personal angel (daimon) and god (theou) were used somewhat interchangeably. By the time of Plato a distinction started to appear, which was explicated in this exchange between Socrates and the priestess Diotima in the Symposium:
“What then is Love?” I asked; “Is he mortal?” “No.” “What then?” “As in the former instance, he is neither mortal nor immortal, but in a mean between the two.” “What is he, Diotima?” “He is a great spirit (daimon), and like all spirits he is intermediate between the divine and the mortal.” “And what,” I said, “is his power?” “He interprets,” she replied, “between gods and men, conveying and taking across to the gods the prayers and sacrifices of men, and to men the commands and replies of the gods; he is the mediator who spans the chasm which divides them, and therefore in him all is bound together, and through him the arts of the prophet and the priest, their sacrifices and mysteries and charms, and all, prophecy and incantation, find their way.
A similar notion of the guardian angel persists to this day, which is known in modern occultism because it was developed into a system of theurgic magic by Mathers in his Book of the Sacred Magic of Abramelin the Mage, the central goal of which is called the Knowledge and Conversation of the Holy Guardian Angel. The aspirant, after a period of ritual purification (similar to the ascetic lifestyle advocated by many of the Gnostic sects) is said to attain mastery over many things in this world. The magical SATOR square, employed therein, was known to ancient magic practitioners, including those of ancient Alexandria. In many ways, we see, the Western esoteric tradition has remained largely intact over the millennia.