Mastema appears in the Book of Jubilees, a Jewish text dated to approximately 170–150 BCE that retells the events of Genesis and the early chapters of Exodus. In it he functions much like the Satan of the Book of Job — an accuser operating within the divine court, granted licence to test and prosecute, and never exceeding the permissions he has been given. He is described as the chief of the spirits of the Nephilim, the disembodied entities of the half-angelic offspring of the Watchers, whose nature is to corrupt the children of men.
His origin as a power in the world is a matter of a bargain. When God prepares to bind all the evil spirits after the Flood, and Noah prays that his descendants be freed from their affliction, Mastema intervenes: he beseeches God to allow him to retain one tenth of these spirits under his command, to tempt and test humanity before the day of judgement, “for the evil of the sons of men is great.” God grants the request. One tenth of the spirits remain, and Mastema commands them. His authority is not seized in rebellion — it is petitioned for, and licensed. This is the theological crux of the figure: his power exists by permission.
Throughout Jubilees, Mastema is the adversarial hand behind the trials of the patriarchs. It is Mastema, not Satan, who urges God to test Abraham with the sacrifice of Isaac. He is the force that seeks to kill Moses on his return to Egypt, and it is Mastema who releases the Egyptian magicians to counter the plagues, and whose powers are credited with the death of the Egyptian firstborn. He is bound while Israel departs Egypt, then loosed to drive the Egyptians into the sea and their doom. In the Dead Sea Scrolls, the Damascus Document refers to the “angel of mastema” — the prosecutorial angel, adversarial by definition. Notably, the text implies he does not fear imprisonment alongside the Nephilim: he is of a different order, an angel who serves rather than a spirit to be bound.
The relationship between Mastema and the figure of Satan is close enough that many readers have treated them as one. In Jubilees, the entity Belial (or Beliar) is mentioned and is probably identical with Mastema; and Mastema's function — the accuser who tests God's servants — is precisely that of the Satan in the Book of Job, rather than the Satan of later Christian tradition who is the uttermost enemy of God. Scholars have suggested that Mastema represents a step in the development of the Devil as a figure independent of God: by transferring to an angel the troubling, adversarial actions attributed to Yahweh in the Torah, the authors of Jubilees remove malice from the Godhead while preserving divine sovereignty. Yet the text stops short of true independence. Ultimately it is God who grants Mastema his demons, and God who sets the limits. Evil is permitted, for a time, without being committed by the divine directly.
The theological distinction is precise: Mastema acts with permission, where the later Satan acts in opposition. It is a difference with a sharp edge — an enemy who works inside the divine order cannot be resisted by defying that order, since defiance only sets one against the very authority he serves.