BoM Jesus Lifted Up on Cross

3 Nephi 27:14; “And my Father sent me that I might be lifted up upon the cross; and after that I had been lifted up upon the cross, that I might draw all men unto me, that as I have been lifted up by men even so should men be lifted up by the Father, to stand before me, to be judged of their works, whether they be good or whether they be evil—”. – 34 AD

John 12:31-33; “Now is the judgment of this world: now shall the prince of this world be cast out. 32 And I, if I be lifted up from the earth, will draw all men unto me. 33 This he said, signifying what death he should die.”

Would the Nephites know what a cross was at this time and if so how did they know? 

The cross was a death weapon used by the Romans and nonexistent in a New World setting. 

The Mormons don’t believe that Jesus paid for sins on the cross so why is this verse in the BoM?