Andrew Murray said this quote
“ What is the reason that many thousands of Christian workers in the world have not a greater influence? Nothing save this—the prayerlessness of their service. In the midst of all their zeal in the study and in the work of the Church, of all their faithfulness in preaching and conversation with the people, they lack that ceaseless prayer which has attached to it the sure promise of the Spirit and the power from on high. It is nothing but the sin of prayerlessness which is the cause of the lack of a powerful spiritual life! ”