OK, so this is REALLY big for me.
I just finished cleaning up my kitchen. Now, I mostly did this for my dad. You see, he loves coming home to a clean house, especially a clean kitchen.
The thing is, me cleaning is also part of living at my house (obviously). It's part of being a family. Everyone pitches in to carry the weight so my mom and dad don't have a second full time job. But, at the same time, I cleaned my kitchen because it would make my dad happy. Not to earn his love or happiness with me, but to do something nice for him.
It's the exact same thing with our Father. We do things for Him not because we have to, but it makes Him happy. It doesn't earn His love for us, but it lets Him know that we love Him back.
In the same way that a husband brings flowers not to prove that he his a husband, but rather to invest in the relationship.
My sonship is never determined by what I do. But my love for my dad inspires me to clean the kitchen to let him know that I love him.