The underpinning of the Christian faith is forgiveness, which admittedly is hard to discern sometimes in watching Christians’ treatment of others; but, for the sake of argument let’s just agree that “those” Christians just haven’t gotten that part of faith yet.
Grace is what we’re given as Christians by the act of Jesus taking our sins on and dying on the cross in our place. An amazing act by a human even if you don’t believe that’s what he did, because HE believed it, and He died believing it.
And those who followed Him believed it, and many of them died horrible deaths believing it too. Like Peter who demanded to be crucified upside-down rather than in the same manner as Jesus because he didn’t feel he didn’t deserve to die like Jesus did. Now that kind of belief merits some serious consideration, what do you believe in strongly enough to continue saying it’s true after your leader is put to death? What do you believe in strongly enough to say I am willing to die to say it? And die in a most hideous manner?
That kind of courage is born by something bigger than earthly concerns, that kind of commitment is not natural to humans; it requires an attachment to a belief in something spiritually universal, like forgiveness.
So why do some people measure forgiveness out in little cups according to some self-designed tally of merit when the giver of forgiveness (God) does not? Jesus died on the cross for all sins, not for those that latter day Christians deem worthy of grace.
God granted grace to all who would accept it, all of us sinners, not those among us who deem that their sins rate more worthy of grace than all the sins of all the other sinners.
An empty hand can’t give grace; how can one give what one can’t accept?