If the Law was perfect, why couldn't it give eternal life and righteousness?
The Law was perfect, and its demands reflected God's holiness, so if a person could keep all Ten Commandments, God could grant eternal life and righteousness. But no person can fulfill it; only Christ Himself kept the Law perfectly. Therefore the Law cannot give life because no one can meet its demands.
Les explains that the Law is not against God's promises. If a law had been given that could give life, then righteousness would have come by the Law. The potential was there because the Ten Commandments contained all the demands of the Holy God. If a human being could have kept all ten, God would have welcomed him into Heaven, since the Law was perfect and such a person would have met God's demands. But the problem is that no person can do it. Nobody can keep those Ten Commandments other than Christ Himself.
Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law.
More Questions
What does Paul mean that if a law could have given life, righteousness would have been by the law?
Paul's reasoning is that if any law had been given that could have given life, then righteousness would have come by the Law — meaning the Law had the potential to give eternal life because all the demands of a holy God were contained in the Ten Commandments.