Joseph Smith understood far more than any other man in this dispensation. Listen to him for a minute.
“Let us suppose a case. Suppose the great God who dwells in heaven should reveal himself to Father Cutler here, by the opening heavens, and tell him, I offer up a decree that whatsoever you seal on earth with your decree, I will seal it in heaven; you have the power then; can it be taken off? No. Then what you seal on earth, by the keys of Elijah, is sealed in heaven; and this is the power of Elijah, and this is the difference between the spirit and power of Elias and Elijah; for while the spirit of Elias is a forerunner, the power of Elijah is sufficient to make our calling and election sure; and the same doctrine, where we are exhorted to go on to perfection, not laying again the foundation of repentance from dead works, and of laying on of hands, resurrection of the dead, &c.
We cannot be perfect without the fathers, &c. We must have revelation from them, and we can see that the doctrine of revelation far transcends the doctrine of no revelation; for one truth revealed from heaven is worth all the sectarian notions in existence.”
You can read those two paragraphs ten times and only gain the barest sense of what is being taught. They are not to be comprehended in a moment, or even in a year. Joseph Smith said “the things of God are of deep import; and time, and experience, and careful and ponderous and solemn thoughts can only find them out” and indeed, the same is true of many of his own great teachings: Time, experience, careful and ponderous and solemn thoughts can only find them out.