It made no difference to Joseph Smith whether he read and was familiar with every doctrine taught by the Apostles; he was under no necessity of framing his teachings therewith that there should be no difference between that which he taught, and that which had been taught, because the same spirit that revealed to the ancient Apostles and Prophets, and inspired them to teach the people, and leave on record their predictions and doctrines, taught him also and enabled him to teach exactly the same truths.
I remember hearing related brother Parley P. Pratt's first interview with the Saints in Fayette, Seneca County, where the Church was organized. Those of you who remember brother Parley know his familiarity with the Scriptures, especially with the prophecies. On that occasion he was called upon to speak; the Prophet Joseph was not present at the time. He brought forth from the prophecies of Isaiah, Jeremiah, Ezekiel and other prophets, abundant proofs concerning the work which the Lord had established through his servant Joseph, a great many of the Latter-day Saints were surprised that there were so many evidences existing in the Bible concerning this work. The Church had then been organized some five months, but the members had never heard from any of the elders these proofs and evidences which existed in the Bible. And, if I remember correctly, he told me that Oliver Cowdery and the Prophet Joseph himself were surprised at the great amount of evidence there was in the Bible concerning these things. The Prophet Joseph was inspired of God to teach the doctrines of life and salvation, and he did so without reference to what the ancient prophets had said. (4)
4) And when ye shall receive these things, I would exhort you that ye would ask God, the Eternal Father, in the name of Christ, if these things are not true; and if ye shall ask with a sincere heart, with real intent, having faith in Christ, he will manifest the truth of it unto you, by the power of the Holy Ghost.(5)
Search the scriptures–search the revelations which we publish, and ask your Heavenly Father, in the name of His Son Jesus Christ, to manifest the truth unto you, and if you do it with and eye single to His glory nothing doubting, He will answer you by the power of His Holy Spirit. You will then know for yourselves and not for another. You will not then be dependent on man for the knowledge of God; nor will there be any room for speculation.(6)