Q. How do we know that Psalm 83 (which, to me, sounds like a prayer, rather than a prophecy) is actually a prophecy of war? What makes that “prayer” a “prophecy” that we know as the Psalm 83 war ?
A. You’re correct in saying Psalm 83 is a prayer, but that doesn’t make it a hypothetical one, such as when we pray for protection against whatever danger might arise. The prayer is too specific in naming the names of Israel’s enemies, even quoting their words.
Nothing that would have fulfilled Psalm 83 has ever happened, so there are two possibilities. Either the prayer was answered pre-emptively and God over ruled the enemy’s plan, or the prayer was for a future time. Until recently we might have accepted the first possibility, but suddenly modern nations occupying the lands of the very enemies Psalm 83 spoke of are surrounding Israel and threatening to attack, and they’re uttering the exact words from Psalm 83:4. Then you have the fact that these enemies, against all logic, will not be involved in a prophecy we know is about an attack against Israel (Ezekiel 38). Why are they missing? These are strong circumstantial indicators that Psalm 83 is a prophecy that will soon be fulfilled.