Here are ten reminders for Christians about the vital need to cultivate a personal prayer life, as articulated by notable ministers from church history.
1. True effectiveness comes not through methods, but through prayer.
A. C. Dixon: When we rely upon organization, we get what organization can do; when we rely upon education, we get what education can do; when we rely upon eloquence, we get what eloquence can do, and so on. Nor am I disposed to undervalue any of these things in their proper place, but when we rely upon prayer, we get what God can do.1
D. L. Moody: Those who have left the deepest impression on this sin-cursed earth have been men and women of prayer.2
E. M. Bounds: What the Church needs today is not more machinery or better, not new organizations or more and novel methods, but men and women whom the Holy Ghost can use — people of prayer, people mighty in prayer.3
2. A man's prayer-life is indicative of the state of his walk with the Lord.
John Owen: A minister may fill his pews, his communion roll, the mouths of the public, but what that minister is on his knees in secret before God Almighty, that he is and no more.4
Charles Spurgeon: I know of no better thermometer to your spiritual temperature than this, the measure of the intensity of your prayer.5
3. Prayer is a vital means of sanctification.
J. C. Ryle: Prayer and sinning will never live together in the same heart. Prayer will consume sin, or sin will choke prayer.6
John R. W. Stott: To pray is not only to be truly godly; it is also to be truly human. For here are human beings, made by God like God and for God, spending time in fellowship with God. So prayer is an authentic activity in itself, irrespective of any benefits it may bring us. Yet it is also one of the most effective of all means of grace. I doubt if anybody has ever become at all Christ-like who has not been diligent in prayer.7
4. Neglect in prayer leads to vulnerability in temptation.
J. C. Ryle: Bibles read without prayer; sermons heard without prayer; marriages contracted without prayer; journeys undertaken without prayer; residences chosen without prayer; friendships formed without prayer; the daily act of prayer itself hurried over, or gone through without heart: these are the kind of downward steps by which many a Christian descends to a condition of spiritual palsy, or reaches the point where God allows them to have a tremendous fall.8
John Owen: If we do not abide in prayer, we will abide in temptation. Let this be one aspect of our daily intercession: “God, preserve my soul, and keep my heart and all its ways so that I will not be entangled.” When this is true in our lives, a passing temptation will not overcome us. We will remain free while others lie in bondage.9
Charles Spurgeon (in a letter to his young son): One of my sweetest joys is to hear that a spirit of prayer is in your school, and that you participate in it. To know that you love the Lord and are mighty in prayer would be my crowning joy; the hope that you do so already is a happy one to me. I should like you to preach; but it is best that you pray; many a preacher has proved a castaway, but never one who has truly learned to pray.10
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5. Busyness is never a valid excuse for neglecting prayer.
Martin Luther: Work, work from early until late. In fact, I have so much to do that I shall spend the first three hours in prayer.11
R. A. Torrey: We are too busy to pray, and so we are too busy to have power. We have a great deal of activity, but we accomplish little; many services but few conversions; much machinery but few results.12
6. Prayer relies on the power of the Spirit to accomplish His work in preaching the Word.
Charles Haddon Spurgeon: Shall I give you yet another reason why you should pray? Hitherto all other means have been used without effect. God is my witness how often I have striven in this pulpit to be the means of the conversion of men. I have preached my very heart out. . . . My hearers, I have done my utmost. . . . Will not your prayers accomplish that which my preaching fails to do? . . . Have we not tried to preach without trying to pray? Is it not likely that the church has been putting forth its preaching hand but not its praying hand? O dear friends! Let us agonize in prayer.13
7. Prayer stamps truth onto the heart.
John Bunyan: The truths that I know best I have learned on my knees. . . . I never know a thing well, till it is burned into my heart by prayer.14
8. Interceding for others reminds us that the Lord Jesus is also interceding for them and for us.
Robert Murray M’Cheyne: If I could hear Christ praying for me in the next room, I would not fear a million enemies. Yet distance makes no difference; He is praying for me.15
9. Prayer knits your heart to people.
William Law: There is nothing that makes us love a man so much as praying for him; and when you can do this sincerely for any man, you have fitted your soul for the performance of everything that is kind and civil toward him.16
Richard Baxter: We must not only pray for ourselves, but we must often pray on behalf of all our hearers. Prayer must carry on our work as well as preaching. He preaches not heartily to his people, who will not often pray for them.17
10. God calls Christians to pray boldly and also to work diligently.
Hudson Taylor: You may work without praying but you can't pray without working.18
George Müller: Here is the great secret of success, my Christian reader. Work with all your might; but trust not in the least in your work. Pray with all your might for the blessing in God; but work at the same time with all diligence, with all patience, with all perseverance. Pray, then, and work. Work and pray. and still again pray, and then work. And so on, all the days of your life. The result will surely be abundant blessing. Whether you see much fruit or little fruit, such kind service will be blessed.19
[Editor's Note: This post was originally posted in 2016 and has been updated.]
 A. C. Dixon. Cited from John Piper, Brothers We Are Not Professionals, 71.
 D. L. Moody, Great Preaching on Prayer, 8:119.
 E. M. Bounds, The Classic Collection on Prayer, 584.
 John Owen. Cited from I. D. E. Thomas, A Puritan Golden Treasury, 192.
 Charles Spurgeon, The Metropolitan Tabernacle Pulpit, 41:518.
 J. C. Ryle, Home Truths, 114.
 John R. W. Stott, Christian Basics, 128.
 J. C. Ryle, Practical Religion, 70–71.
 John Owen, Triumph Over Temptation, 165.
 Charles Spurgeon. Cited from Charles Ray, The Life of Charles Haddon Spurgeon, 381.
 Martin Luther. Cited from the 1923 Cyclopedia of Religious Anecdotes, 303.
 R. A. Torrey, How to Obtain Fulness of Power in Christian Life and Service, 81.
 Charles Spurgeon, Metropolitan Tabernacle Pulpit, 5:311.
 John Bunyan. Cited from Charles Spurgeon, Spurgeon on Prayer, 285.
 Robert Murry M’Cheyne, The Works of Rev. Robert Murray McCheyne, 138.
 William Law, A Serious Call to a Devout and Holy Life, 220.
 Richard Baxter, The Reformed Pastor, 218.
 James Hudson Taylor. Cited from D. L. Moody, One Thousand and One Thoughts from My Library, 63.
 George Müller. Cited from Frederick G. Warne, George Müller, 227.