Paul went into detail emphasizing the magnitude of God's "gift" of salvation by contrasting it with the condemnation faced by man because of his sin (Romans 5:14-21). When man sinned he brought into his reality the consequence of sin. The ultimate consequence, of course, is death (Genesis 2:17; Romans 6:23).
But connected with that is the further consequence that sinning makes man a sinner. As a sinner he is guilty with no way to remove from himself the guilt of his own sin. That's where God, in His love and grace, stepped in and sent His perfect Son to the cross. In giving the life of Jesus, God satisfied the terms of the debt for man's sin (Hebrews 9:28). Man, as a guilty sinner, could not satisfy those terms himself. God did it for him.
It's incredible to contemplate. God offers the gift of salvation. But, in order to be able to offer that gift God first had to give the life of His Son. Without this greatest of all gifts mankind would be hopelessly lost in the condemnation of sin. How strange that so many choose to continue in sin and thus remain condemned. How careless, how foolish! But it's also disrespectful to God and the unbelievable sacrifice that He made in giving the life of His Son. How terrible it will be to face judgment having rejected the greatest gift ever given.