"We are never so much in our element as when we are engaged in prayer to God, for then we are acting agreeably to our creation and redemption."
Andrew Fuller (1754–1815) as found in The Works of Andrew Fuller, though not tied to a single specific sermon.
"True prayer is neither a mere mental exercise nor a vocal performance. It is far deeper than that—it is a spiritual transaction with the Creator of Heaven and Earth."
Charles Spurgeon (1834–1892) This is a paraphrase from Spurgeon’s sermon "The Power of Prayer," delivered on March 11, 1866, and recorded in The Metropolitan Tabernacle Pulpit, Volume 12.
"Prayer is a sincere, sensible, affectionate pouring out of the heart or soul to God, through Christ, in the strength and assistance of the Holy Spirit, for such things as God hath promised, or according to the Word, for the good of the church, with submission, in faith, to the will of God."
John Bunyan (1628–1688) From Bunyan’s treatise A Discourse Touching Prayer (also known as I Will Pray with the Spirit), published in 1662.
"The Spirit helps the saints in prayer, when they know not what to pray for as they ought; he suggests their wants unto them, and makes intercession for them according to the will of God."
John Gill (1697-1771) Derived from Gill’s Exposition of the Bible, specifically his commentary on Romans 8:26–27.
"Expect great things from God; attempt great things for God."
William Carey (1761–1834) The Journal and Selected Letters of William Carey, edited by Terry G. Carter (2000).
"Prayer is an act of religious worship, and an ordinance of God; it is a calling upon his name, and should be performed in the name of Christ, by the assistance of the Spirit, and with a view to the glory of God."
John Gill (1697-1771) From A Body of Practical Divinity (Book I, Chapter 24: "Of Public Prayer")
"Prayer is the slender nerve that moves the muscle of omnipotence."
Charles Spurgeon (1834–1892) From (The Metropolitan Tabernacle Pulpit, Vol. 34, "The Secret Power in Prayer," 1888)