D&C 22

 The Savior taught - 

"...all old covenants have I caused to be done away in this thing; and this is a new and an everlasting covenant, even that which was from the beginning."  (Doctrine and Covenants 22:1)

This suggests to me that the Lord presented the "new and and an everlasting covenant" in each dispensation, even in the beginning.

He also states - 

"...although a man should be baptized an hundred times it availeth him nothing, for you cannot enter in at the strait gate by the law of Moses, neither by your dead works."  (Doctrine and Covenants 22:2)

In my mind, "dead works" are ordinances and covenants not performed by His authorization, His priesthood keys, or by His Church.