Why were people convicted by the Law?
The Holy Spirit convicted people by the Law to reveal their need, because they could not do it on their own. The Law exposed that their root problem was not merely what they were doing but who they were—sons of Adam, born with a sin-bent personality—so self-reformation was for nothing until God did what only God can do.
Les explains that the Holy Spirit was moving upon the population, convicting men by the Law of their need of something because they couldn't do it on their own. The Law's conviction exposed that the root problem is not what we're doing but who we are—sons of Adam. Every baby born is in the same place Adam was after he fell, with a sin-bent personality that can try to clean itself up but is all for nothing until God does what only God can do.