For it is expedient that an atonement should be made; for according to the great plan of the Eternal God there must be an atonement made, or else all mankind must unavoidably perish; yea, all are hardened; yea, all are fallen and are lost, and must perish except it be through the atonement which it is expedient should be made.
For it is expedient that there should be a great and last sacrifice; yea, not a sacrifice of man, neither of beast, neither of any manner of fowl; for it shall not be a human sacrifice; but it must be an infinite and eternal sacrifice.
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.
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.
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.
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.
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.
And thus mercy can satisfy the demands of justice, and encircles them in the arms of safety, while he that exercises no faith unto repentance is exposed to the whole law of the demands of justice; therefore only unto him that has faith unto repentance is brought about the great and eternal plan of redemption.
Source: Alma 34:9-16; The Book of Mormon: Another Testament of Jesus Christ