Whose sins were laid on Christ on the cross?
All the sin of humanity—from Adam until the last person who will ever live in time—was laid on Christ on the cross. God poured out His wrath for sin on Him and judged it, so that sin debt is paid, with rejecting the Gospel being the only sin that leads to eternal doom.
Les teaches that Christ's crucifixion was not just another crucifixion among thousands. What made it unique was that He was the Creator God Himself, who took on human flesh to go to that cross. On that cross, God poured out all of His wrath for sin. All the sin from Adam until the last person who will ever live in time was laid on Christ, and God judged it. Even the vilest, lost, wicked people have their sins already atoned for and paid for. The only reason they would go to an eternal doom is if they reject the Gospel, because the sin debt has been paid and finalized once and for all.