Can a person have a testimony of a doctrine and not live it? Conversely, can a person not live a doctrine and still have a testimony of it? I suppose the question really comes down to (as so many seem to) a matter of definitions. That is, is a testimony an all-or-nothing thing? Is it binary, like a light switch? Can you only be "a little bit" pregnant? Only mostly dead?
A testimony is indeed something that can grow, like that mustard seed - so I suppose it is not binary (though it does need to start somewhere). However, the real crux of my first two questions above is: what is the result (or inevitable destiny) of a testimony which is not "lived"? We know that it is like a foreign language (or many other skills) - "use it or lose it."
The question originally popped into my head during Elders Quorum today. The particular subject was that of genealogy (that is, "doing the work" for the dead). I have a testimony of that sacred duty; however, it has been a while since I actually DID anything about it (that is, set aside time to do the necessary research) that I felt a certain shame in saying to myself that I had a testimony of it. For, I reasoned, if I really had a testimony of it, I would be acting upon it, would I not? I act upon all the other things of which I have a testimony, don't I? Then I got to thinking, and in a cross between honest self-assessment and over-self-criticism, I wondered how I can claim to have a testimony of something like, say, charity - which I feel I don't do a very good job of acting upon.
Maybe it is too harsh to say that a lack of constant and perfect action regarding a particular doctrine is evidence of a lack of testimony of it, but it does bear consideration that failure to act can and does lead to a withering of testimony (which can become a vicious circle). Don't get me wrong, I have no doubts about the truth of any Gospel principle, only doubts in my own choices from time to time. I know I need to do better in many areas (don't we all?), but I am reminded that Joseph Smith said (in Lectures on Faith) that faith is a principle of action. Thus, in order to increase faith (testimony), we must act upon those beliefs we hold.
So, lest I forget the incredibly powerful feelings I experienced when I did the temple work for my family members (I've done the first 9 closest relatives in my family), I really need to prioritize doing more. I hope I can apply that motivation to all of the areas where I fall short.