Grace is love that is given to those who are not worthy. Grace is God showing nothing but love and mercy when we deserved nothing but anger and judgment. It is God bending toward us in infinite love. Grace was seen when God gave heaven's best to save earth's worst. God does not owe us anything.
Salvation is a free gift.
Do not mix up grace with law. We are not saved by keeping the law. We are saved by grace. Law gives us a work to do. Grace tells us that a work has been finished.