Rule of Law

• WWizards of the Coast2019-07-12
  Official Ruling
  Rule of Law looks at the entire turn to see if a player has cast a spell, even if Rule of Law wasn’t on the battlefield when that spell was cast. Notably, you can’t cast Rule of Law and then cast another spell during the same turn.
• WWizards of the Coast2019-07-12
  Official Ruling
  If you cast a spell that was countered, you can’t cast another spell during the same turn.

Rulings via Scryfall