Alma 43:46

and they were doing that which they felt it was the duty which they owed to their God; for the Lord had said unto them, and also unto their fathers, That inasmuch as ye are not guilty of the first offence, neither the second, ye shall not suffer yourselves to be slain by the hands of your enemies.

They were doing what they felt was their duty to God. The Lord had said to them and to their fathers: If you do not attack first or second, you do not have to let your enemies kill you.

They were doing what they felt was their duty to God. The Lord had told them—and their ancestors—“As long as you’re not the ones who start the fight, you don’t have to let your enemies kill you.”