Sheep were an important image here because Christ’s suffering and death was likened to the sacrifice of the Passover lamb. Isaiah had prophesied that this suffering Lord would be sacrificed, like the sheep killed in the temple. If the priests of Noah understood what that meant, Abinadi could have proven his case that this was a shadow of things to come.
It is also clear from Isaiah 53 that the Savior will have power to make intercession, and Abinadi explained the nature of that intercession by using the phrase that he will "stand betwixt them and justice" (Mosiah 15:9). The word "intercession" (v. 8) literally means "to sit between." Christ will sit between us and justice to hold off execution of our punishments while giving us time to repent. Mercy will not be inconsistent with justice, because justice will occur eventually, but not before the time of intercession. There will be an interceder who will facilitate the redemption that Isaiah referred to in Mosiah 12:23. The one who will intercede is Christ.