How does the poet use allusion in this poem?

Byron uses allusion in this poem to create a sense of place and to generate an understanding of whose side God is on in the battle. He references "the blue waves" in "deep Galilee," which the reader would understand as a reference to the Galilee where Jesus was born. The Biblical allusions continue in the third stanza when the poet describes how "the Angel of Death . . . breathed in the face of the foe," a striking image which suggests that the "foes" are subjected to the power of God acting upon them.
The final stanza demonstrates the most consistent use of allusion, with the poet referencing several notable "heathen" cultures from the Old Testament who suffer at the hands of God (whom they disavowed): the worshippers of Baal and the Gentiles (non-Jews, people who were not the promised children of God) were "melted like snow" in the eyes of God, who did not smile upon them. The widows of Ashur, also, are set wailing in pain. Ashur was an East Semitic god, another opponent of the Lord whose power is clearly nothing compared to his.