The root word in excellence is "excel." To excel means to go beyond. Beyond what? Beyond expectations. And people rarely go beyond what they have to do, unless purpose is present. Purpose leads to passion, and passion leads to excellence. So if you consistently want to produce excellence, then focus primarily on the purpose (the deeper "why").
If you are in a leadership role, have regular discussions about the team's purpose and how each person's unique role contributes to it.
Takeaway: Purpose leads to excellence.