How would you reject grace?
How to reject grace? Let us count the ways.
Blaspheming the Holy Spirit, for one; deciding on what is good or evil for ourselves or others without reference to God; creating one's own church.
Basically choosing hell over heaven.
St. Paul (1 Cor 3:12) says that it is up to every man to accept grace or to reject grace. That choice must be made every second of every minute of every day. It cannot be a one-off event. It must be continuous - to love God with your whole heart, your whole soul and your whole strength. One single event is enough to reject grace and you must take steps to regain it or else you remain in a state of sin or in a state without grace.