19 ¶And he took bread, and gave thanks, and brake it, and gave unto them, saying, This is my body which is given for you: this do in remembrance of me. 20 Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you. (Luke 22:19-20)
It struck me as I read this recently what it meant for Jesus to say that the cup (or the wine in it) was the new testament in His blood which was shed for us.
Up to that point, the major way that covenant Israel had an ordinantial testimony of the Spirit about the redemption of the Messiah came from offering animal sacrifices and eating the covenant meal of meat from it.
Here Jesus declares that from that point onward, covenant Israel would obtain that witness of the Spirit—the nourishing, healing, renewing witness working to sanctify them--from the sacrament. That is amazing. It's subtle, but incredible.
Who is the only one who can tell the Holy Ghost to change which ordinances to testify during and do sanctifying work during? Only another member of the Godhead. It's a major change of systemic spiritual blessing declared right there. Absolutely revolutionary.