Joseph and Hyrum
Joseph and Hyrum died for the Truth of God. Joseph Smith has indeed done more in the world for the salvation of mankind than any other person, Jesus Christ excepted. Joseph Smith translated the Book of Mormon by the power of God into English, that it might stand as a second witness to Jesus Christ the Redeemer, along with the Bible. The Book of Mormon also stands as a testament to the world that Joseph Smith was in fact a Prophet, because the only way it could have been brought forth is how Joseph Smith said it was - by revelation, nothing more nor less. Hyrum Smith stood by his brother's testimony of the Book of Mormon no less quietly, for he also knew it is true, for the Holy Ghost told him so.
I know Joseph Smith was a Prophet of God, and that the Church he was an instrument in restoring is the only true and living Church upon the face of Earth, for the Lord God hath spoken it: "And also those to whom these commandments were given, might have power to lay the foundation of this church, and to bring it forth out of obscurity and out of darkness, the only true and living church upon the face of the whole earth, with which I, the Lord, am well pleased, speaking unto the church collectively and not individually" (D&C 1:30). Also, "For thus shall my church be called in the last days, even The Church of Jesus Christ of Latter-day Saints" (D&C 115:4).
The Nauvoo Illinois Temple
This House of the Lord was built on the same spot of ground of the original. This House of the Lord is a second witness (along with the Book of Mormon) to the prophetic calling of Joseph Smith, in that the only Church on Earth to teach the fulness of the ordinances of the Priesthood is The Church of Jesus Christ of Latter-day Saints. The covenants within the Endowment ceremony have not changed since Joseph Smith gave the ordinance in the second story of his Red Brick Store in Nauvoo on 4 May 1842, which building is now owned by a church who believes in Joseph Smith in name only - they have rejected him as a Prophet of God, as has the rest of the the world.
Conditional Salvation For Men in this Age
The only way to be saved is through Jesus Christ the Son of God. He, and He alone, is the Author of Salvation and Exaltation. However, for mankind now living, one must accept Jesus Christ as the Savior of the World and also Joseph Smith as a Prophet of God (whether in this life or the next), or they cannot be saved. Jesus Christ must be accepted because He is the Way, the Truth, and the Life.
Joseph Smith must be accepted because he was the humble instrument Jesus Christ used to restore His Church to Earth again. Through Joseph Smith the Priesthood Authority was brought from the Heavens and given to The Church of Jesus Christ of Latter-day Saints, and only to that Church. All others are pretenders. This I solemnly proclaim in humility and by the power of the Holy Ghost, for He is my witness that I speak the truth. Search the revelations and commandments that have been given to The Church of Jesus Christ of Latter-day Saints, and you will find I speak the truth. In the name of Jesus Christ, amen.