One man cannot live upon the revelations given to another

"the word spoken to Noah was not sufficient for Abraham, or it was not required of Abraham to leave the land of his nativity and seek an inheritance in a strange country upon the word spoken to Noah, but for himself he obtained promises at the hand of the Lord and walked in that perfection that he was called the friend of God. Isaac, the promised seed, was not required to rest his hope upon the promises made to his father, Abraham, but was privileged with the assurance of his approbation in the sight of heaven by the direct voice of the Lord to him.

"If one man can live upon the revelations given to another, might not I with propriety ask, why the necessity, then, of the Lord speaking to Isaac as he did, as is recorded in the 26th chapter of Genesis? For the Lord there repeats, or rather promises again, to perform the oath which he had previously sworn unto Abraham. And why this repetition to Isaac? Why was not the first promise as sure for Isaac as it was for Abraham? Was not Isaac Abraham’s son? And could he not place implicit confidence in the word of his father as being a man of God?

"Perhaps you may say that he was a very peculiar man and different from men in these last days; consequently, the Lord favored him with blessings peculiar and different, as he was different from men in this age. I admit that he was a peculiar man and was not only peculiarly blessed, but greatly blessed. But all the peculiarity that I can discover in the man, or all the difference between him and men in this age, is that he was more holy and more perfect before God and came to him with a purer heart and more faith than men in this day."

"The same might be said on the subject of Jacob’s history. Why was it that the Lord spake to him concerning the same promise after he had made it once to Abraham and renewed it to Isaac? Why could not Jacob rest contented upon the word spoken to his fathers?...

"...the Lord hear [will] my prayers and listen to my cries as soon as he ever did to theirs if I come to him in the manner they did[.]"  (Letter from Joseph Smith to his uncle Silas Smith, Sept. 26, 1833, Kirtland, Ohio; in Lucy Mack Smith, “The History of Lucy Smith, Mother of the Prophet,” 1845 manuscript, pp. 229–32, Church Archives.)