We have been given the choice to separate ourselves from our old identity in Adam and accept freedom through the work on the cross of Jesus Christ. The choices we make in our new identity in Christ are still our own choices and we can still use that free will to sin. If you're asking yourself why not keep living the life of sin that was so easy before? The answer is because it is fundamentally not who we are anymore after being freed from enslavement to sin after receiving salvation in Christ.