Those who become Gods must practice polygamy

The only men who become Gods, even the Sons of God, are those who enter into polygamy. Others attain unto a glory and may even be permitted to come into the presence of the Father and the Son; but they cannot reign as kings in glory, because they had blessings offered unto them, and they refused to accept them. (Brigham Young, 19 August 1866, JD 11:26)