If someone could keep all ten commandments, would God let them into heaven?
Yes—if a person could perfectly keep all ten commandments, the Law could give life, and that person would have met God’s demands, so God would welcome them into His Heaven. The Law is perfect; the problem is that no human being can keep it. Only Christ Himself did.
Les explains Paul’s question: is the Law against God’s promises? He says no, it enhances them. The point is that if a law could have given life, then righteousness would have come by the Law. Since all the demands of the Holy God were in the Ten Commandments, if a human being could have kept all ten, God would have let him into His Heaven, because the Law was perfect and fulfilling it would meet 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.