"...all old covenants have I caused to be done away... and this is a new... covenant..."

"The old covenant was one of bondage while the new is one of freedom (Gal. 5:1). The new one is the "new and living way" (Heb. 10:20)."
"We are being told by some of our brethren today that there has been, and is, but one covenant. If this is so, the priesthood of Jesus Christ is totally invalidated, so is the new covenant, and we all are still under the law of Moses."
"This false doctrine of one continuing covenant from the time of Abraham till now is summarily refuted by the priesthood of Christ after the order of Melchizedek. Jesus was not of the tribe of Levi, but of Judah (Heb. 7:14). Therefore, he could not have been a Levitical priest of the first covenant, or the law of Moses (8:9). His priesthood changed the priesthood "after the order of Aaron" (7:11), and by necessity, therefore, changed the law (7:12) that governed "the Levitical priesthood" (7:11,12). The seventh chapter of Hebrews completely demolishes the false doctrine of those who advocate the one covenant theory"

D&C 22:1
"Behold, I say unto you that 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."
Melchizedek