I've always found the "license to sin" thing of modern pop-Christianity to be a bit odd. The churches I've engaged with as an adult have focused on this - 1. Salvation frees from the deathly burden of sin and cannot be earned or revoked once given, but is paltry when viewed from an eternal perspective. 2. Salvation aside, sin is a hinderance to accessing God on a personal level, aka being filled with His Spirit. 3. Doctrinal teaching makes us aware of our sin and how to function both in avoiding sin and pursuing righteousness. 4. Sin must be confessed directly to God, followed by repentance and pursuit of righteousness as prescribed by biblical doctrine. 5. The value of the life of righteousness and spiritual maturity is a demonstration to God of how we value our salvation. In essence, it's the gift we give back to God as gratitude, much like the present you give your mother for her birthday - it will be loved and accepted no matter how small, but we will be more fulfilled by the greater gift we can give in response.