Andrew F. Ehat describes the "more sure word of prophecy" as the most precise explanation of making one's calling and election sure.
Andrew F. Ehat, and Lyndon W. Cook. The Words of Joseph Smith: The Contemporary Accounts of the Nauvoo Discourses of the Prophet Joseph (Provo, UT: BYU Religious Studies Center, 1980), 283 n. 27
Comparison between 2 Peter 1:17 and 2 Peter 1:19. This definition of making one's calling and election sure, the definition given in the 27 June 1839 discourse, and the material at note 31 & of this discourse are the clearest and most precise explanations of this important spiritual experience.