To this day, Jews and Christians around the world use the text of Psalm 91 to ward off evil spirits and demons. Gerrit Vreugdenhil investigated the historical context in which this Old Testament song came about, and why this text appeared so early on amulets and in magical texts.
In Chile or other Christian South American countries, you should not be surprised if a Bible open to Psalm 91 is on a bedside table or by a hospital bed. You often see him hanging on small paintings at the entrance of a house or on porcelain objects in the form of an open book.
Apparently Psalm 91 is assigned a magical power that protects people against all kinds of evil, evil spirits, demons and other scum. The magical power of the text appears in the earliest Jewish history. Psalm 91 is just one of 150 songs in the Old Testament book of Psalms. Gerrit Vreugdenhil (UU) carefully analyzed the word usage in this psalm and reconstructed how the ancient Israelites thought about demons and spirits way before Christ. He discovered that Psalm 91 must once have been written specifically as a defense against demons.
In the main source text, the Old Testament, there is little to be found about how people thought about spirits and demons at the time the psalms were written. But the most recent archaeological excavations show that amulets, pendant jewelry, as well as images of Egyptian gods such as Horus and the dwarf god Bes were widely used to ward off evil demons. In the world of ancient Israel, demons were omnipresent.
Vreugdenhil then analyzed the text of the psalm. The psalm presupposes that "someone" is afraid of evil, which may be of demonic origin ("Do not fear the terror of the night, nor the arrow that flies at you by day" Ps. 91.5)). A frightened person is addressed, but by whom? Which characters or actors play a role in the psalm? What will happen to them?
'Terror of the night'
There are four actors in the psalm; the fearful man, the Jewish deity jhwh, one who is authorized to speak on behalf of jhwh and a sort of general audience to whom the story is told. The psalm does not speak of king, temples or the people or other themes from the official religion of the people of Israel. That is why the psalm was probably used outside the official temple cult, within family circles.
The large number of amulets found in places of familial home cults show that the threat of (demonic) evil was taken seriously. Moreover, it appears from Vreugdenhil's linguistic analysis that terms such as 'disposition of the night', 'arrow', 'lion' and 'viper' were associated with demonic powers.
Verse 9a is about the power of YHWH over the evil powers of the world. Because a priest or representative of YHWH speaks in the psalm, the psalm was probably written for cases of illness and demonic disaster that exceeded the power of the family religious experience. The power and protection of YHWH is in the foreground. The psalm acknowledged that there are demonic powers in the world, and it was written with that idea in mind. But these demons have to give up against the almighty YHWH. This double message makes Psalm 91 traditionally popular for chasing away evil spirits.