The main effect is that it remains on the field for 3 of your opponent's turns. As long as "Swords of Revealing Light" remains on the field, your opponent cannot attack.
"Swords of Revealing Light" is not only useful when your opponent has stronger monsters than you do. It is also useful when you have a powerful Effect Monster, like "Cure Mermaid", and you want to protect it from being attacked.
The other effect of "Swords of Revealing Light" is to flip your opponent's monsters face-up when it is played. This is a 1-time effect and does not last for the 3 turns. But it is a great way to see what your opponent has on the field and force any Flip Effects to activate.