If you indeed obey his voice

Here "voice" represents what the angel says. Alternate translation: "If you carefully obey what he says" (See: rc://en/ta/man/jit/figs-metonymy)

an enemy to your enemies and an adversary to your adversaries

These two phrases mean the same thing and are used for emphasis. (See: rc://en/ta/man/jit/figs-parallelism)