Found this as well from a Mormon site:
Christ is our judge. But he has also called some people to play a role in judging and reigning over others. For example, Christ told the Apostles that they would sit as judges over the House of Israel (Matt. 19:28). The Bible further records that the Saints would also sit as judges (1 Cor. 6:2,3; Rev. 20:4). Joseph Smith, as the chief apostle of this dispensation, has a similar privilege. Christ's chosen leaders participate in the judgment in some way - and thus those in this dispensation of the Gospel have some accountability to Joseph Smith as well, who holds the keys of this kingdom now as Peter did of old. (Those old stories about people meeting Peter at the Pearly Gates derived from this concept, no doubt.) When Brigham Young said that no one would get into heaven without Joseph's approval, I understand that he is saying that Joseph will play an apostolic role in the judgment and that those of this dispensation will be accountable for how they received or rejected the powerful testimony that Joseph offered, crowned with the Book of Mormon and sealed with his own blood. Ultimately all judgment and authority is committed to the Son and the Father, but portions of it are delegated to men through the Priesthood. Joseph's role, like those of the early Apostles, is clearly subordinate to that of the Son in this matter - and in any other matter, as well.
