Preachers commonly took a biblical passage as their sermon topic. JS was stating that this was the first time he had preached on the book of Revelation. (Sturtevant, Preacher’s Manual, 1:68; Stowe, “On Expository Preaching,” 384.)
Sturtevant, S. T. The Preacher’s Manual; or, Lectures on Preaching. . . . 2nd ed. 2 vols. London: Richard Baynes, 1834.
Stowe, Calvin Ellis. “On Expository Preaching and the Principles Which Should Guide Us in the Exposition of Scripture.” Biblical Repository and Quarterly Observer 5, no. 18 (Apr. 1835): 384–402.
TEXT: Possibly “for”.