When Joseph and Oliver commissioned and ordained twelve Apostles, there were told they were not actually Apostles until they had obtained their own knowledge of Christ. When one is baptized by water, they are not baptized by fire until a time of God's choosing. When one goes through the veil of the temple, the person does not enter heaven on the other side until they actually fulfill the blessings offered to them in the temple. When one is ordained to the Melchizedek priesthood, he does not actually have that most Holy Priesthood until he proves himself acceptable and God Himself gives it to him.
"You have been indebted to other men, in the first instance, for evidence; on that you have acted; but it is necessary that you receive a testimony from heaven for yourselves; so that you can bear testimony to the truth of the Book of Mormon, and that you have seen the face of God. That is more than the testimony of an angel. When the proper time arrives, you shall be able to bear this testimony to the world. When you bear testimony that you have seen God, this testimony God will never suffer to fall, but will bear you out; although many will not give heed, yet others will. You will therefore see the necessity of getting this testimony from heaven.
"Never cease striving until you have seen God face to face. Strengthen your faith; cast off you doubts, your sins, and all your unbelief; and nothing can prevent you from coming to God. Your ordination is not full and complete till God has laid His hand upon you. We require as much to qualify us as did those who have gone before us; God is the same. If the Savior in former days laid His hands upon His disciples, why not in latter days?" (Oliver Cowdery, HC v 2, ch 13, p 195)
The Difference Between Knowing and Believing
When Joseph and Oliver commissioned the twelve, they said they were indebted to others for the evidence on which they acted, and they would be until they spoke with God face-to-face.
These twelve, until they obtained this knowledge, only had the Gift of the Spirit to believe on the words of those who knew. We would also have eternal life if we knew Jesus Christ is the Son of God.
"To some it is given by the Holy Ghost to know that Jesus Christ is the Son of God, and that he was crucified for the sins of the world. To others it is given to believe on their words, that they also might have eternal life if they continue faithful." (D&C 46:13-14)
"And this is life eternal, that they might know thee the only true God, and Jesus Christ, whom thou hast sent." (John 17:3)