I believe that spiritual as well as natural greatness depends in a high degree on the faithful use of means within everybody’s reach. Of course I do not say we have a right to expect a miraculous grant of intellectual gifts; but I do say, that when a person is once converted to God, his progress in holiness will be much in accordance with their own diligence in the use of God’s appointed means. And I assert confidently that the principle means by which most believers have become great in the church of Christ — is the habit of diligent private prayer.
Look through the lives of the brightest and best of God’s servants, whether in the Bible or not. See what is written of Moses and David and Daniel and Paul. Mark what is recorded of Luther and Bradford the Reformers. Observe what is related of the private devotions of Whitefield and Cecil and Venn and Bickersteth and McCheyne. Tell me of one of the goodly fellowship of saints and martyrs, who has not had this mark most prominently — they were men of prayer. Depend on it, prayer is power. Prayer obtains fresh and continued outpourings of the Spirit. He alone begins the work of grace in a person’s heart. He alone can carry it forward and make it prosper. But the good Spirit loves to be entreated. And those who ask most — will have most of his influence.
Adapted from J.C. Ryle, A Call to Prayer