Bhagwad Gita
Chapter 4, Verse 12
काङ्क्षन्तः कर्मणां सिद्धिं यजन्त इह देवताः।
क्षिप्रं हि मानुषे लोके सिद्धिर्भवति कर्मजा।।4.12।।
Men in this world desire success in fruitive activities, and therefore they worship the demigods. Quickly, of course, men get results from fruitive work in this world.