If "The Sanctuary in the Sky" is on the field, you can activate this card by discarding 1 LIGHT monster from your hand to the Graveyard. Choose 1 card your opponent controls or 1 in their hand (you can look at their hand), and send it to the Graveyard.
You must have The Sanctuary in the Sky on the field to activate Light of Judgement. The best way to search out The Sanctuary in the Sky is with Zeradias, Herald of Heaven which can also be used as a beater if you already have The Sanctuary in the Sky on the field. Planet Pathfinder is another way to search out your field spell but will use up your normal summon for the turn.
Not only you can avoid "when this card is destroyed" effect, but also, if you choose hand card, you gets to see your opponent's entire hand, allowing you to pick a handtrap and remove it away before it can be used.
Yeah, a lot of people just say "trash" when this card is a good normal card, nothing bad about it although it's also not the best now (latest errata makes DW effect goes off since it discards from hand instead of send.....)
too bad this isn't counter trap or it would be OP.