How are the Law given to Israel and the message of Grace to us not contradictory?
They are not contradictory because God's Word contains no contradictions; what appears contradictory is actually a change in God's program. Under Law, God dealt with Israel one way; under Grace, He deals with us another way. The message differs because the operation changed, not because Scripture contradicts itself.
Les teaches that there are no contradictions in Scripture. He explains that what God told Israel under Law seems to contradict what He tells us under Grace, but it is not a contradiction; it is a change in operation or program. Les also notes that he does not lift a verse out of context or twist it; if he cannot keep everything together, he leaves it alone. So the Law and Grace differ because God's program changed, not because His Word contradicts itself.