2 Nephi 3

In the 2nd chapter of the  Book of Abraham we again learn of the special covenants the Lord made with Abraham which were extended to Isaac and Jacob.  In the 3rd chapter of 2nd Nephi, we learn of special covenants the Lord made with Joseph.  Even thought the Lord made special covenants, we also know that there are essential and necessary covenants for Eternal Life that man must enter into to obtain such.  Ancient Joseph shared that -

"...Thus saith the Lord unto me: A choice seer will I raise up out of the fruit of thy loins; and he shall be esteemed highly among the fruit of thy loins.  And unto him will I give commandment that he shall do a work for the fruit of thy loins, his brethren, which shall be of great worth unto them, even to the bringing of them to the knowledge of the covenants which I have made with thy fathers."  (Book of Mormon | 2 Nephi 3:7)

One of the purposes of the Prophet Joseph Smith then was to restore knowledge concerning these essential and saving covenants as well as -

"...unto him will I give power to bring forth my word unto the seed of thy loins—and not to the bringing forth my word only, saith the Lord, but to the convincing them of my word, which shall have already gone forth among them."  (Book of Mormon | 2 Nephi 3:11)

I repeat again the value of covenants where Nephi said -

"...I, Nephi, beheld the power of the Lamb of God, that it descended upon the saints of the church of the Lamb, and upon the covenant people of the Lord, who were scattered upon all the face of the earth; and they were armed with righteousness and with the power of God in great glory."  (Book of Mormon | 1 Nephi 14:14)

It is the knowledge of these covenants that were restored.