Why will believers reign in life forever?
Because of the one man, Christ Jesus, and what He accomplished, not because of their own works. Those who receive abundance of grace and the gift of righteousness shall reign in life, eternal life forever, in contrast to death reigning through Adam's one offense. It is God's gift, not human attainment.
Les explains that salvation is not something people must attain, work for, or grasp at; it is right in front of every human being, like the door to the sheepfold at ground level, attainable to anyone. In the passage he is reading, if by one man's offense death reigned, much more those who receive abundance of grace and the gift of righteousness shall reign in life. This reign is not like old death's reign; believers will reign like a king, in eternal life forever and forever, because of the one Christ Jesus, not because of what they do but because of what He accomplished. Adam was the federal head of the human race and plunged everyone into condemnation, but the second Adam accomplished everything necessary to bring fallen man back to Himself. The only difference now is that there must be an exercise of will.
For if by one man’s offence death reigned by one; much more they which receive abundance of grace and of the gift of righteousness shall reign in life by one, Jesus Christ.)