The one thing I might add is that I believe that how we grow when we lift, parallels how we grow spiritually. My concept of the spirit, informed by my particular religious tradition and personal experience, is that the spirit is a material thing (call it a state of mass/energy if you like), rather than some "immaterial" thing, and that it responds to our choices/actions by increasing or decreasing in light/intelligence/goodness/unity with God.
What Are Spiritual Changes?
Positive spiritual changes are, I think, directly apprehensible to us. We know when we've done good because our spirit expands in response to our choices and we are aware of it. One comes to know whether a given course is a godly one by attempting it and then feeling within their own soul, the fruits of that effort.
I sometimes think of "Truth" as a state of being, as opposed to some externally verifiable state of affairs, although that latter definition is more commonly used. It's an approach that includes the danger of moral relativism, but I'm at peace with it.
I'm also pretty convinced that at some point after death we will be able to directly apprehend the spiritual condition of others. As St. Paul puts it, "then shall [we] know even as also [we are] known."
I envision it precisely the same way that we can look at each other today with our physical eyes and see whether or not we've put in the work and exercised the self-control to sculpt our physical body.
It may be an odd thing to say, but what cemented this particular vision of things in my own mind was a sort of un-looked for epiphany I had on a regular morning bike ride. When it isn't below 30 degrees, I typically ride my bike two mornings per week along an 8-mile course that includes five hills. One particular morning while climbing the last hill I was sufficiently distracted by thinking of some un-related event that I failed to notice that I'd topped the hill and gone onto the flat. Ordinarily, the physical strain of going up that last hill would have held my attention.
In that instant I realized that an incremental physical change had occurred as a result of consistent, disciplined effort. Going up that hill was simply easier. I was more free to go on to something a little more challenging. It was a change that was apparent to me even if it was so small that no one else would have noticed.
And at the same instant that this thought occurred to me, I considered that past conscious efforts at emotional/spiritual improvement yielded analogous feelings spiritually, that, in fact, the spirit seemed to behave in a remarkably similar fashion as the physical body. It was one of those moments when your mind opens up, grasps something without logical proof, and simply accepts it as correct.
The Difference Between Spiritual Effort & Physical Effort
Since then I have often considered the parallels between spiritual effort and physical effort. You don't increase your squat without a certain amount of pain, nor do you leap from squatting 200-to-400 pounds over night. Likewise, you don't learn to be patient with your spouse or children without accepting the pain of admitting that you have hurt them occasionally through impatience and without exercising self-control and positive choice on a consistent basis.
There are workouts in which I notice that the last rep is incrementally easier, although my arms still shake, or I pause at the sticking spot just as long as I did last time. No spotter could tell a difference, but I can. And there are times when, internally, I am slightly more patient with my children, although they don't know that I am making that choice.
In the aggregate, though, over time and through hard work, the change is real, and solid, and it becomes a source of deep-running, underpinning happiness. And eventually those around you do take note and are attracted to that which you have built, which might be called character.
2004 Bodybuilding.com New Years Guide.