Doctrine

Reading Elder McConkie's April 1982 "The Doctrine of the Priesthood", I realized I had no idea what "doctrine" means. I watched a video and pondered, and came to the conclusion that

Doctrine - the rules for becoming more like Him.

You can break it down more specifically, for example, the Doctrine of the Priesthood is "the rules for using the Priesthood to become more like Him."

Tangentially related, my favorite quote from McConkie's talk:

"we have power, by faith, to govern and control all things, both temporal and spiritual"

Probably one of the most empowering beliefs I've ever heard.