As I see it, there are two reasons to strive for excellence in whatever it is that we do for God.
First, that which we produce [be it music, writing, manufacturing, teaching, supervising--whatever we do] can reflect the very glory of God. If we can bring the very best of our talents and giftedness, this excellence radiates the beauty of God. God is the giver of every good and perfect thing. So when good things come from our hands, they pulse with God's life and goodness and beauty.
Second, our efforts to bring our best are accepted as worship to God. Our laborous efforts, intensely trying to get things right in order to honor God, is worship. When we bring God our best work, our serious effort, our attention to detail, we worship.
And whatever you do, whether in word or deed, do it all in the name of the Lord Jesus, giving thanks to God the Father through him. [Colossians 3:17]