What did Les teach that "you are forgiven all your trespasses" means?
It means Christ's death paid the sin debt for every human being. Since Hebrews says He tasted death for every man, and Paul says if one died for all, then all were dead, His death paid the sin debt for all trespasses. Therefore they will not be faced with their sin as what caused them to stand before the Great White Throne.
Les teaches that when Scripture says "you are forgiven all your trespasses," it means Christ's death paid the sin debt for every human being. He stresses that when Christ died, He paid the sin debt, and Hebrews says He tasted death for every man. Paul in II Corinthians chapter 5 says that if one died for all, then all were dead. Les concludes that Christ's death paid the sin debt for every human being, so they are not going to come up and be faced with the fact that their sin is what caused them to stand before the Great White Throne.
And you, being dead in your sins and the uncircumcision of your flesh, hath he quickened together with him, having forgiven you all trespasses;