I see God's mercy as a strong cord securely attached to every single one of us to keep us from falling away from him, with us hanging from the cord in perfect balance. Every time we sin, whether we are believers or not, we cut and weaken that cord. When we repent and ask to be forgiven, the cord is healed again. Anyone who chooses to sin continuously and not repent is to sever that cord. To me, rejecting God's mercy is as serious a sin as limiting it, believing that he cannot save you, if not more so.