Ether 5:1 the things which I have sealed up...touch them not in order that ye may translate
Chapter 5 seems to be a message directed specifically to Joseph Smith and the latter-day Gentiles. The translator is explicitly instructed of Moroni to leave the sealed portion alone. We have no indication that Joseph was ever disobedient to this command or that he was even curious about the content of the sealed portion.
Bruce R. McConkie
"It was returned by Joseph Smith to Moroni, its divinely appointed custodian. Nor did even Joseph Smith either read or translate it. [The sealed portion of the plates.] We know of no one among mortals since Mormon and Moroni who have known its contents. It was known among the Nephites during the nearly two hundred years of their Golden Era. But for the present, the book is kept from us; only the portion upon which no seal was placed has been translated." (A New Witness for the Articles of Faith, p. 443 as taken from Latter-day Commentary on the Book of Mormon compiled by K. Douglas Bassett, p. 493)
Ether 5:2-3 ye may show the plates unto those who shall assist
Again, this message was written specifically for Joseph Smith. When the prophet translated this portion of the record, he was prompted to show the plates unto three witnesses. This was according to the promise which had been previously given to the prophet, in addition to your testimony, the testimony of three of my servants...shall go forth with my words that are given through you. Yea, they shall know of a surety that these things are true, for from heaven will I declare it unto them (DC 5:11-12). However, the demonstration of the record was to be done according to the will of the Lord, for the record was to be shown by the power of God (v. 3).
Joseph Smith
"In the course of the work of translation, we ascertained that three special witnesses were to be provided by the Lord, to whom He would grant that they should see the plates from which this work (the Book of Mormon) should be translated; and that these witnesses should bear record of the same, as will be found recorded, Book of Mormon, page 581 [Book of Ether, chapter 5, verses 2, 3 and 4, p. 487, edition 1920], also page 86 [II Nephi, chapter 11, verse 3, p. 73, edition 1920]. Almost immediately after we had made this discovery, it occurred to Oliver Cowdery, David Whitmer and the aforementioned Martin Harris (who had come to inquire after our progress in the work) that they would have me inquire of the Lord to know if they might not obtain of him the privilege to be these three special witnesses; and finally they became so very solicitous, and urged me so much to inquire that at length I complied; and through the Urim and Thummim, I obtained of the Lord for them the following: (DC 17)
'Behold, I say unto you, that you must rely upon my word, which if you do with full purpose of heart, you shall have a view of the plates, and also the breastplate, the sword of Laban, the Urim and Thummim, which were given to the brother of Jared upon the mount, when he talked with the Lord face to face, and the miraculous directors which were given to Lehi while in the wilderness, on the borders of the Red Sea.
And it is by your faith that you shall obtain a view of them, even by that faith which was had by the prophets of old.
And after that you have obtained faith, and have seen them with your eyes, you shall testify of them, by the power of God.'"
(History of the Church, 1:52-53, see also DC 17:1-3)
Ether 5:3 unto three shall they be shown by the power of God
The plates had to be shown to the three witnesses by the power of God. This means that Joseph Smith could not just show them the plates and ask them to testify. This would not do. Others would contend that he had fashioned some ancient appearing record in order to dupe the three witnesses into a false testimony. In order to prove to the world that Joseph Smith was not a magician and the greatest deceiver of his day, the Lord would reveal the truth of the Book of Mormon to the three witnesses by the indisputable power of God.
"It has been the boast of so-called sleight-of-hand performers that they can duplicate every trick of spiritists, no matter how astounding; but here is a plain divine manifestation of which no human art, or ingenuity, can furnish an imitation." (Reynolds and Sjodahl, Commentary on the Book of Mormon, 6:111)
Accordingly, the three witnesses were not just shown the plates. Instead, they were shown a vision from God in which they saw an angel, saw a light from heaven, and heard a voice. Appropriately, Moroni himself appeared to them and showed them the gold plates, the sword of Laban, the Liahona, the breastplate, and the Urim & Thummim (see commentary on the three witnesses and DC 17:1).
Joseph Smith
"...we beheld a light above us in the air, of exceeding brightness; and behold, an angel stood before us. In his hands he held the plates which we had been praying for these to have a view of. He turned over the leaves one by one, so that we could see them, and discern the engravings thereon distinctly. He then addressed himself to David Whitmer, and said, 'David, blessed is the Lord, and he that keeps His commandments;' when, immediately afterwards, we heard a voice from out of the bright light above us, saying, 'These plates have been revealed by the power of God, and they have been translated by the power of God. The translation of them which you have seen is correct, and I command you to bear record of what you now see and hear.'" (History of the Church, 1:54-55)
Testimony of the Three Witnesses
"...we...have seen the plates...And we also 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. And we also testify that we have seen the engravings which are upon the plates; and they have been shown unto us by the power of God, and not of man. And we declare with words of soberness, that an angel of God came down from heaven, and he brought and laid before our eyes, that we beheld and saw the plates, and the engravings thereon; and we know that it is by the grace of God the Father, and our Lord Jesus Christ, that we beheld and bear record that these things are true. And it is marvelous in our eyes..."
Orson Pratt
"...the Lord confirmed the truth of the Book of Mormon unto many witnesses in such a way, and by such means, that it was impossible for them to have been deceived;...the testimony of these witnesses stands good until it can be refuted; [and] no man can be justified in rejecting this testimony until he can show that it is false...Now, no one has ever attempted to bring any direct negative testimony; this, indeed, would be impossible, unless the witnesses themselves should deny their former testimony, and this they have not done. And those who have attempted to condemn their testimony from the nature of the message itself, have only exhibited their own weakness and folly. Upwards of twenty years (now 170 yrs.) have passed away, and no man has, as yet, been found able to prove the Book of Mormon or the testimony of its witnesses false." (Pamphlet: "Divine Authenticity of the Book of Mormon," p. 65)
Ether 5:4 all this shall stand as a testimony against the world at the last day
Nobody likes to hear the phrase, "I told you so!" But those who reject the Book of Mormon will be shown their folly at the last day. In essence, they will hear "I told you so" from the Savior who said, ye shall know that it is I that speaketh, at the last day (Ether 4:10). They will hear "I told you so" from the three witnesses whose declaration shall stand as a testimony against the world at the last day. They will hear "I told you so" from every member of the Godhead, for the Father, and the Son, and the Holy Ghost [will] bear record. Finally, they will hear "I told you so" from Moroni who warned, ye shall know that I have authority when ye shall see me, and we shall stand before God at the last day (v. 6). Who else will be there to condemn the unbeliever? Will it be Joseph Smith? Will it be the missionary who first delivered the book? Will it be a teacher, a bishop, or a friend? Finally, it will be the unbeliever himself; convinced of his own error, he will be condemned by his own conscience.
Bruce R. McConkie
"Though men may reject the teachings of the apostles and prophets concerning Jesus Christ and his gospel, yet those very teachings shall rise to condemn the unbelievers in the day of judgment. That is, the words of the apostles and prophets shall stand as a testimony against unbelievers at the judgment bar of Christ. (2 Ne. 33:10-14; Moro. 10:27-29, 34.)" (Doctrinal New Testament Commentary, 1:330)