The nature of grace is that it free. God expects nothing and asks for nothing in return.
The reality of grace is that it is a gift. The nature of a gift is that it is given freely with no conditions of reciprocity.
The nature of grace is such that we cannot and it is not good for us to try to repay God.
A lot of theologies fear making grace so free in that it will lead to a life of debauchery in their opinion. The reality is that a true grace from God comes with the power of God to live a changed life.
Only a counterfeit grace upon receiving it would wish to continue a life of sin. Of course surely we sin as Christians and fall frequently, but the nature of it is that it pains us and is not the orientation of our life.