When I first started lifting it was strictly to impress girls, but that is pretty standard fare for a 15-16 year old guy.
Now that I am an old married man with children I primarily lift weights for me. I like the way I feel after a hard workout, and lifting also helps make my chronic spine pain a lot more tolerable.
I enjoy being strong, when I stopped lifting I missed strength the most by far. It is nice being able to make heavy **** move with little effort.
I also like how my kids look at me in awe when I am working out, lifting what is to them immovable masses of iron. Kids only think that their Dad is smartest, strongest, wisest,toughest man for so long before they learn that he is just human.
It is also nice to be noticed by women, even though there is no chance of anything sexual taking place.
When you take all of these things together it adds up to me just overall feeling better. Not just physically, but on all levels. It is important to remember though that we don't get our value as humans through our physiques, but there is certainly nothing wrong with feeling good about ourselves.