[First Presidency to Lowry Nelson]
... The basic element of your ideas and concepts seems to be that all God's children stand in equal positions before Him in all things. ... Indeed, some of God's children were assigned to superior positions before the world was formed. We are aware that some Higher Critics do not accept this, but the Church does. Your position seems to lose sight of the revelations of the Lord touching the preexistence of our spirits, the rebellion in heaven, and the doctrines that our birth into this life and the advantages under which we may be born have a relationship in the life heretofore. From the days of the Prophet Joseph Smith even until now, it has been the doctrine of the Church, never questioned by any of the Church Leaders, that the Negroes are not entitled to the full blessings of the Gospel. Furthermore, your ideas, as we understand them, appear to contemplate the intermarriage of the Negro and White races, a concept which has heretofore been repugnant to most normal-minded people from the ancient patriarchs till now. God's rule for Israel, His Chosen People, has been endogamous. Modern Israel has been similarly directed. We are not unmindful of the fact that there is a growing tendency, particularly among some educators, as it manifests itself in this area, toward the breaking down of race barriers in the matter of intermarriage between the whites and blacks, but it does not have the sanction of the church and is contrary to Church doctrine.
[Source: First Presidency, Letter to Lowry Nelson, as quoted in Minutes of the Apostles of The Church of Jesus Christ of Latter-day Saints, 1835-1951, Electronic Edition, 2015]