As a child, I'd often do my chores only either to get a prize or to make amends for a wrong I did. Growing up, I slowly found myself motivated to do the same chores to show my family that I love them. The same chores that took life from me before slowly became a source of joy for me.
I believe it's the same with our faith. As infants in our faith, we observe merely out of fear or familiarity; bothersome sacrifices we do just because we felt we have to. As we mature in our faith and love for God, we find ourselves doing the same things not out of mere obligation, but as expressions of our love; we move from doing things for ourselves, to doing things for God, asking nothing in return; from slaves who wish sacrifices to end, to friends who heartily wish we can do more.
It's a long way for me, that's for sure. How about you? Where are you in your spiritual growth?