Ether 12:10 reflects the teaching Moroni knew from Alma 13:10: “Now, as I said concerning the holy order, or this high priesthood, there were many who were ordained and became high priests of God; and it was on account of their exceeding faith and repentance, and their righteousness before God, they choosing to repent and work righteousness rather than to perish.”
Verse 11 declares that it was the faith of the Israelites that allowed them to enter into the covenant known as the law of Moses. Jesus Christ fulfilled that law, and it was done by faith. How might that have happened? Christ entered his final days on earth understanding what would befall him. The earthly consequences were absolutely clear. The heavenly benefits had been declared, but required faith so that he could act with an eye to the heavenly benefit rather than the earthly distress and pain.
The language of Ether 12 is unique, but the principle that links faith and miracles was taught from the beginning, and throughout, Nephite history. See 2 Nephi 26:13; 27:23; Mosiah 8:18; Alma 37:40; 3 Nephi 19:35.