What is the resolution between Gaap the divine soldier and Swords of Revealing Lights?

Answer 1

If Gaap is face-up beforehand, all other monsters will already be in face-up attack mode due to his effect. Swords of Revealing Light won't do anything to them, except stop them attacking while it remains in play.

If Gaap is face down, then Swords of Revealing Light will switch him and any of that players' Set monsters face up. Gaap's continuous effect will switch them all into attack mode, as well as any monsters controlled by the opponent.

Note when a card says battle positions can't be changed, this means manually, by players. They can still be switched by card effects, so you can use Book of Moon while Gaap is in play. However Gaap's effect that forces monsters into attack positon is continuous and will immediately revert such monsters to face-up attack mode once more, unless it was himself who was flipped face-down.

Answer 2

If Gaap is controlled by the opponent, then Gaap and the opponent's other cards will be flipped face-down. Gaap only prevents manual battle position changes, not ones from an effect.

If Gaap is controlled by the player who activated Swords of Concealing Light, the opponent's monsters will be flipped face-down. Gaap will then return them to face-up attack mode as per his continuous effect. Again, the restriction against changing battle positions only applies to manual changes, not changes by effect. Swords of Concealing Light will not stop Gaap from switching them.