From John Piper’s Brothers, We Are Not Professionals:

Without extended, concentrated prayer, the ministry of the Word withers. And when the ministry of the Word declines, faith (Rom. 10:17; Gal 3:2, 5) and holiness (John 17:17) decline. Activity may continue, but life and power and fruitfulness fade away. Therefore whatever opposes prayer opposes the whole work of ministry.