Why does God's grace lead us to want to please Him?

Les teaches that grace is not license. Just because God has declared us forgiven, justified, redeemed, and reconciled, that does not mean we now live as we please. Instead, it brings such a love requirement and such a debt for such love that we should want to do everything we can to please Him. Therefore, we should not live unto ourselves, but unto Him who died for us and rose again. This is the Gospel, plain as day. Les also explains that this doctrine is based on Christ's death, burial, and resurrection, and that Paul no longer looks back at Christ's earthly ministry as the basis for our doctrines. Old Testament saints were justified, but not on the same basis that we are under grace.