One has to understand what living under the law was and what the age of grace is. Moses was no liar but by Christ's death and resurrection we no longer live under the law. During the OT days forgiveness was dependent on keeping the law. Payment of sin's penalty to satisfy holy justice was done by blood sacrifice. Grace means that sin is not held against the sinner. God the Son is our substitute, Christ died in our place.
But there is surely a need to keep to the laws? We can't break them, or disregard them, on the basis that 'grace' will pull us through at the end?