What is wrong with trying to earn eternal life by works?
Trying to earn eternal life by works is wrong because it denies that all people are sinners through Adam, totally separated from God, and spiritually dead. It assumes human effort can merit God's favor, but such people will not get in; eternal life depends on Christ's sacrificial death for the whole human race.
Les explains that when people try to make eternal life theirs by works, they are flatly denying this. They are not admitting they have been totally separated from God or that they are dead spiritually. Instead, they still think whatever they do will merit favor with God and get them in, but they will not. Since all are sinners by birth from Adam, the whole human race was dead in sin and needed Christ's sacrificial death.