1 Nephi 4:18

"Therefore I did obey the voice of the Spirit, and took Laban by the hair of the head, and I smote off his head with his own sword."
1 Nephi 4:18


This has always been an interesting scripture to me, and although it isn't any more harsh than anything in the old testament, it still is hard to understand sometimes, especially since the Book of Mormon was written for our day, right?  Why there are exceptions to huge things like "thou shalt not kill?"  I think one of the reasons that we have it is to show us that God is the author of the laws.  He knows absolutely and without question what is right and what is wrong, and how things work.  And maybe it is also to show us that we need to listen to the spirit.  Following the letter of the law isn't always going to work, even though it is a great guideline.  we have to get to the point where we are actually communicating with God every day and following his promptings, no matter what.  And really, until we get to that point, we have no idea where the exceptions are.  We have to assume we are part of the rule unless God tells us otherwise.
It's kind of like learning another language perhaps.  You learn a lot of rules and phrases and how to put them together, and so you are living the letter of the law... or at least attempting to, as far as you are able.  But until you immerse yourself in the culture, and hang out with people who are speaking the living language every day... you don't know many of the exceptions... you don't even know what is funny and what isn't.  :)  and, it might take a lifetime to actually get to the point where you can make up a new word, or break rules at the right time and the right place to get a laugh or actually communicate an idea better.  God, as the original native speaker of the language, knows which rules he can break, and what things are hilarious, and what things are serious.  We're trying to pick it up as we go along... but the more we talk to God as the native speaker, the more we will understand how the language of the Gospel works, and where there are double meanings and start to understand the poetry and the beauty of the whole thing... and when we have God there as translator, then we will understand—even when the information coming in doesn't quite make sense to us as students in Gospel 101.