Anyone who has been a
Mormon for some time is familiar with this "couplet". However, the
Mormon church does in fact hide this idea from outsiders. It is not included in the six
missionary discussions given before baptism. In addition,
Gordon B. Hinckley, the church's president, recently said to an outsider in relation to this principle, "I don't know that we teach it". Being the
prophet, he has to be aware that it has been taught in the church since the 1830s. This is evidence that he is uncomfortable with the teaching and didn't want to discuss it with an outsider.
This principle was expounded by Joseph Smith, the founder of the LDS church, in his famous "King Follet discourse". Everything that Joseph Smith taught is accepted as doctrine by Mormons, and therefore so is this principle, although it seems that in recent times there has been a tendency away from it, and it is no longer discussed as often as it once was.