Heber C. Kimball tells the Saints that a person is not in the "true vine" if they reject Brigham Young as a Prophet; they are to have faith in his words.
Heber C. Kimball, "Faith in the Priesthood—Fruits of Faith—Laying Up Grain—Gleaning—The Holy Ghost—Tree of Life, Etc.," Journal of Discourses, 26 vols. (Liverpool: Asa Calkin, 1858), 5:172–73
No man can believe in "Mormonism," except he believes in the man that leads the Church of God—in the man that holds the keys of life and salvation pertaining to this people . . . So it is impossible that a man or a woman who disbelieves that brother Brigham is a Prophet—that holds God's representative and holds the keys of his kingdom pertaining to this people, can retain the Holy Ghost and partake of the life and sap of the true vine. Such persons have no faith of the genuine bearing kind, and consequently there are no works to correspond . . . How shall we manifest our faith by our works? I will speak of that a little further; and I cannot speak the truth as it is in Christ Jesus, without I censure many of you. I will ask those who have been here for four, seven, and eight years past, and from the day that we came into these valleys, if they have proved by their works their faith in the words of the Prophet Brigham?