Sin and Accountability

Hebrews 3:12-14
3:12 See to it, brothers and sisters, that none of you has an evil, unbelieving heart that forsakes the living God. 3:13 But exhort one another each day, as long as it is called “Today,” that none of you may become hardened by sin’s deception. 3:14 For we have become partners with Christ, if in fact we hold our initial confidence firm until the end.
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Sin will drag me down and drown me. It will suffocate my soul until my heart turns to stone in unbelief. They way to avoid sin is to be accountable to other believers so that we can encourage each other. Then we can combat sin's deceitful lies and avoid the hardened hearts and blackened souls. Also, is it possible that we will only share in Christ's mercy if we hold fast to our faith "firm until the end"? A question debated by many theologists. Can an individual turn their back on their faith in Christ's redemptive work, returning to sin and the old creation, and forfeit eternity? Or, does such a lifestyle reveal that the person never actually believed in Christ's death, Resurrection, and return from the beginning? I am not sure yet.