Here is a quote that describes is very well for me.
There is a vitality, a life force, an energy, a quickening that is translated through you into action, and because there is only one of you in all of time, this expression is unique. And if you block it, it will never exist through any other medium and it will be lost. The world will not have it. It is not your business to determine how good it is nor how valuable nor how it compares with other expressions. It is your business to keep it yours clearly and directly, to keep the channel open. You do not even have to believe in yourself or your work. You have to keep yourself open and aware to the urges that motivate you. Keep the channel open. ... No artist is pleased. [There is] no satisfaction whatever at any time. There is only a queer divine dissatisfaction, a blessed unrest that keeps us marching and makes us more alive than the others Martha Graham
I also think of a quote from Paul in Romans 1::20
20 For since the creation of the world God's invisible qualities—his eternal power and divine nature—have been clearly seen, being understood from what has been made, so that people are without excuse.
The creation is a reflection of God's eternal power and divine nature.
Painting the beauty of his creation can be a form of worship for me.
Why we do things is almost as important as what we do.