Alma 34

Amulek taught the poor of the Zoramites -

"...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." (Book of Mormon Alma 34:9)

And that this atonement -

"...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." (Book of Mormon Alma 34:10)

For -

"...there can be nothing which is short of an infinite atonement which will suffice for the sins of the world." (Book of Mormon Alma 34:12)

I've pondered the meaning of an "infinite and eternal" atonement. First of all the Savior declared -

"...for Endless is my name." (Doctrine and Covenants Section 19:10)

So then would Eternal and Infinite be His name. Therefore, the great and last sacrifice is the Atonement of the Savior. But in addition to that, the atonement is literally eternal and infinite in every aspect including time, space, and coverage. The King Benjamin said to his people -

"...the Lord God hath sent his holy prophets among all the children of men, to declare these things to every kindred, nation, and tongue, that thereby whosoever should believe that Christ should come, the same might receive remission of their sins, and rejoice with exceedingly great joy, even as though he had already come among them." (Book of Mormon Mosiah 3:13)

This verse suggests that the children of men may receive a remission of sins "even as though he had already come among them." Since agency has been an eternal gift, why would not the "infinite atonement" had been available in a pre-existent state as if He had already come in the flesh. With agency being available throughout the eternities, for those who believe in Christ, might not the atonement be also available throughout the eternities, suggesting it to be "infinite and eternal".