The Mormon cannot explain, cannot reason or demonstrate, there is no apologetic to convince, his position is indefensible by ordinary means and so he must simply declare that he knows.
To a Mormon reason demands that something is going on or how could anyone reject the force of testimony? “You’ve been talking to Mike Thomas!” Mormons speak about "those who leave the church but can't leave the church alone."
To a Mormon the only possible explanation for doubt is the insidious influence and growth of anti-Mormons. It is unthinkable that Mormonism could be wrong in any respect, ipso facto, the Mormon rests his case.