Alma 34:11 - 34:15
Alma 34: 11 Now there is not any man that can sacrifice his own blood which will atone for the sins of another. Now, if a man murdereth, behold will our law, which is just, take the life of his brother? I say unto you, Nay.
It is not the plan that one person can sacrifice his own life that will atone for another’s sins. If a person kills another, can a sibling allow themselves to die for their crime? Obviously the answer is no.
Alma 34: 12 But the law requireth the life of him who hath murdered; therefore there can be nothing which is short of an infinite atonement which will suffice for the sins of the world.
But the law, which is in place among the Nephites, requires the murder to be executed. So someone else with the power to atone for all individual sins must be in place.
Alma 34: 13 Therefore, it is expedient that there should be a great and last sacrifice, and then shall there be, or it is expedient there should be, a stop to the shedding of blood; then shall the law of Moses be fulfilled; yea, it shall be all fulfilled, every jot and tittle, and none shall have passed away.
Therefore such a sacrifice must be put into place which will be the last time blood is sacrifice for sins such as dictated in the law of Moses. The purpose of the law of Moses was to keep in the minds of the people of the coming of the Messiah and His sacrificing His life and shedding His blood instead of animals. When Christ dies, the need for animal sacrifice will end. The people no longer need to remember by ritual the sacrifice of the Son of God. It will have already taken place and the sacrament will take its place.
Alma 34: 14 And behold, this is the whole meaning of the law, every whit pointing to that great and last sacrifice; and that great and last sacrifice will be the Son of God, yea, infinite and eternal.
That was the purpose of the law of Moses. The sacrifice of the animals was a similitude of the future sacrifice of the Son of God. And his sacrifice will apply to every person ever born on this earth.
Alma 34: 15 And thus he shall bring salvation to all those who shall believe on his name; this being the intent of this last sacrifice, to bring about the bowels of mercy, which overpowereth justice, and bringeth about means unto men that they may have faith unto repentance.
Thus the sacrifice of the Son of God will apply to all that believe on His name. The intent is to overcome the demands of justice which calls for all men to pay for their transgressions. If a man repents of his sins the sacrifice of the Son of God will cover the demands of justice on their behalf.