Of the 11 "official" witnesses to the Book of Mormon, John Whitmer came closest to denying his testimony. Which is why he's a favorite of mine.
In his 1836 final column as editor of the church publication "Messenger and Advocate," Whitmer bore witness of the plates and the Book of Mormon:
"I desire to testify to all that will come to the knowledge of this address," he wrote, "that I have most assuredly seen the plates from whence the Book of Mormon is translated, and that I have handled these plates, and know of a surety that Joseph Smith, Jr., has translated the Book of Mormon by the gift and power of God."
Shortly thereafter, though, when the Kirtland Bank failed and he was excommunicated, Whitmer became doubtful, skeptical, even cynical.
When he encountered Theodore Turley, the church's business agent — who courageously remained in Missouri in order to wind up Mormon financial affairs after the Saints had been expelled under threat of extermination — Whitmer joined with others to ridicule Turley's continued faithfulness.
Turley responded by charging Whitmer with inconsistency. Had he not once borne strong testimony of the Book of Mormon? Where was his faith now?
Still surrounded by his mocking friends, Whitmer admitted, "I handled those plates; there were fine engravings on both sides. I handled them."
Thus, even in his darkest, most doubting hour, Whitmer affirmed that Joseph Smith had possessed engraved metal plates.
Then why was he now allied with critics of the church? Because, he said, he couldn't actually confirm the translation of that strange writing. "I cannot read it, and I do not know whether it is true or not."
In this context, it's vital to remember that while the Three Witnesses to the Book of Mormon saw an angel and heard the voice of God confirming the truthfulness of the Book of Mormon to them ("we … know that they have been translated by the gift and power of God, for his voice hath declared it unto us; wherefore we know of a surety that the work is true"), the Eight Witnesses did not. They went out into a clearing in the woods where they saw and "handled" the plates. That's all. Their experience was relatively mundane, much more limited in character.
Thus, when John Whitmer, at his own darkest point, declared that he could not personally verify the translation but that he had, in fact, held and examined the plates, he was sticking to, and reaffirming, his experience as one of the Eight Witnesses.
And, not long thereafter, he was back to declaring, rather often and sometimes very emotionally, his conviction that the Book of Mormon was true and that it had been translated by the supernatural gift and power of God. (Records still survive of such declarations from up to at least six months prior to his death in 1878.)
In 1861, Jacob Gates spent roughly four hours talking with him, and, afterward, indicated in a journal entry that, while the witness didn't like polygamy and hadn't rejoined the church, John Whitmer "still testified that the Book of Mormon is true and that Joseph Smith was a Prophet of the Lord. He also said that he believed that … Brigham Young was carrying out the doctrine and system which Joseph Smith taught."
At his passing, the local newspaper published an obituary of him, reflecting on his 40-year residence in Caldwell County after the expulsion of the Mormons: "Mr. Whitmer remained at Far West and has since been a highly respected and law abiding citizen."
Why does this matter? John Whitmer's testimony doesn't, by itself, prove the Book of Mormon true. But it is an important indicator pointing in that direction. It greatly strengthens the probability that Joseph Smith actually possessed the plates he claimed to possess and that his claims rest on more than simply personal, subjective hallucination. They involve other people. But there's no evidence for a conspiracy, and, anyway, the bigger a conspiracy is, the more difficult it is to keep it secret and together. Moreover, where did Joseph Smith and his supposed co-conspirators get all that gold?
John Whitmer's testimony contributes to a strong cumulative case for the truthfulness of the Restoration and for God's tangible involvement in it.