Mark 9:23 Commentary - Whedon's Commentary on the Old and New Testaments
23. If thou canst believe An echo of the man’s expression, If thou canst do anything. The man had evidence which required him to have and to use a proper amount of faith. As God does not require our first faith without giving us a first evidence, so our Lord first gave prior evidence of his divinity in order to create a first faith. But when that was done, the condition of the exercise of faith was an inexorable demand. Our Lord thus performed, as we may say, two classes of miracles.
All things are possible to him that believeth When our Lord says “all things,” we are to understand what classes of things he is speaking of, in which he includes all. And the condition (“to him that believeth”) belongs not to every rash and presumptuous belief, that the mind, not in communion with God, may conjure up. The belief and the grant to prayer of which Jesus speaks belong perhaps to the world in which he speaks, namely, the religious and spiritual world. And the belief of which he speaks is that faith of which God grants the power. All things within its sphere are possible to that faith; for God will not grant power to faith for things which he will not make possible.
Consult other comments:
Mark 9:23 - The Greek Testament
Mark 9:23 - Joseph Benson’s Commentary on the Old and New Testaments
Mark 9:23 - Calvin's Complete Commentary
Mark 9:23 - The Cambridge Bible for Schools and Colleges
Mark 9:23 - Adam Clarke's Commentary and Critical Notes on the Bible
Mark 9:23 - Companion Bible Notes, Appendices and Graphics
Mark 9:23 - Expository Notes of Dr. Constable (Old and New Testaments)
Mark 9:23 - Ellicott's Commentary for English Readers (Old and New Testaments)
Mark 9:23 - The Expositor’s Greek Testament by Robertson
Mark 9:23 - Garner-Howes Baptist Commentary
Mark 9:23 - Geneva Bible Notes
Mark 9:23 - John Gill's Exposition of the Entire Bible
Mark 9:23 - Gnomon of the New Testament
Mark 9:23 - Henry Alford's Greek Testament
Mark 9:23 - Biblical Illustrator Edited by Joseph S. Exell
Mark 9:23 - Jamieson, Fausset and Brown's Commentary Critical and Explanatory on the Whole Bible
Mark 9:23 - Expositions Of Holy Scripture by Alexander MacLaren
Mark 9:23 - Church Pulpit Commentary
Mark 9:23 - Commentary Series on the Bible by Peter Pett
Mark 9:23 - Robertson's Word Pictures in the New Testament
Mark 9:23 - A Popular Commentary on the New Testament
Mark 9:23 - John Trapp's Complete Commentary (Old and New Testaments)
Mark 9:23 - The Treasury of Scripture Knowledge
Mark 9:23 - Vincent's Word Studies in the New Testament
Mark 9:23 - Whedon's Commentary on the Old and New Testaments
Whedon's Commentary on the Old and New Testaments

Daniel D. Whedon (1808-1885) was a prominent university professor, theologian, and author. He served as Professor of Ancient Languages at Wesleyan University in Connecticut; as Professor of Rhetoric at the University of Michigan; and as editor of the Methodist Quarterly Review from 1856 to1884. He authored numerous books including Commentary on the New Testament (New York: Carlton & Porter, 1860); Commentary on the Old Testament (New York: Nelson & Phillips, 1873); What is Arminianism? (Toronto: W. Briggs, 1879); and Essays, Reviews, and Discourses (New York: Phillips & Hunt, 1887).