Joseph's sermon of August 13, 1843, addressing salvation of children of parents who have been sealed.
B.H. Roberts, History of The Church of Jesus Christ of Latter-day Saints, 7 vols. (Salt Lake City, UT: Deseret News Press, 1909), 5:530
Four destroying angels holding power over the four quarters of the earth until the servants of God are sealed in their foreheads, which signifies sealing the blessing upon their heads, meaning the everlasting covenant, thereby making their calling and election sure. When a seal is put upon the father and mother, it secures their posterity, so that they cannot be lost, but will be saved by virtue of the covenant of their father and mother.