Psalm 55:18 (ESV)

18 He redeems my soul in safety from the battle that I wage, for many are arrayed against me.

He saves my soul; he protects me in the battles that I wage. For a crowd is going against me.

The author is assured that God will help him, also when many people turn against him. Now, he does not speak about just one opponent. Perhaps his former friend was able to recruit many more people to attack the author. Being arrayed sounds like being lined up, as in an army.