God's grace is not cheap, it cost Him His Son. Tom goes through Matthew 5-7 to show us what it looks like to truly follow Jesus and keep our eyes fixed on Him.
Many American churches have bought into "swiping a grace credit card" in which we act like we want and do what we want because we have a "credit card" to swipe for grace. In contrast, costly grace calls us to truly follow Jesus Christ. When we are following Jesus, we can't do anything without Him. If we lose focus on Him, we no longer feel his presence. Following Jesus means He has to go with you to work and go with you wherever you go. You don't need to know where you are going, just follow Jesus.
Before Jesus tells us what he wants us to do in Matthew 5, He says that we are the salt of the earth and the light of the world. Jesus then tells us what it looks like to follow Him.