Pelagianism, named after the heretic Pelagius, is the belief that Adam’s sin was his alone and his descendants are born into the world innocent as Adam was before his fall in contrast to Augustine’s doctrine of original sin. Because we are not by nature fallen or depraved, we have the ability to merit salvation. God’s saving grace and the cross of Christ are not absolutely necessary for salvation. Pelagius argued that it would be unjust for God to give commands that we are unable to carry out. Since God demands of us perfection, we must be able to live without sin in this life. What lawgiver gives laws that are impossible to keep? Therefore, he argued that we have the natural ability to live in sinless perfection and be admitted into God’s presence on the basis of our obedience to the law.
It is true that we are called to be holy as God is holy because God demands of us perfection (Lev 19:2). Because he does not change, the righteous standard we are held to cannot change. But it does not logically follow that because God demands of us something we are able to carry it out. God calls upon us to circumcise our heart, yet he alone can bring about regeneration (Deut 10:6; 30:6; Jer 4:4; Col 2:11). God commands people to make for themselves a new heart, yet he alone can take out the heart of stone and give them a heart of flesh (Ezek 18:31; 36:26). He tells us to be sinlessly perfect as he is perfect, yet the Bible knows nothing of sinless perfection in this life (Matt 5:48; Jas 3:2). We are called to love God with all our heart, yet our heart often condemns us (Matt 22:37; 1 John 3:20). He calls us to repent, yet he must grant repentance (Acts 17:30; 2 Tim 2:25). We are called to believe in Christ, yet our faith must be granted as well (Acts 16:31; Phil 1:29). Unbelievers are rebuked for their hard and impenitent hearts, yet God must open their heart (Acts 16:14; Rom 2:5). Jesus called upon the man with a withered hand to stretch it out even though he had no natural ability to do so (Matt 12:13). The power from God to stretch it out came with the command. So likewise, the power to repent and believe comes from the Holy Spirit in the call to salvation.
Pelagianism errs in not recognizing that our fallen state does not change God’s righteous character. Because God is perfectly righteous and holy, he demands of us the same thing. Our inability to not sin does not negate our responsibility and guilt toward God as his creatures. Pelagianism wrongly assumes that responsibility implies ability and constructs a theology based around libertarian free will that is not affected by the fall. But the Bible teaches that God supplies the ability for his people to believe during the preaching of the gospel and gives them the Holy Spirit to cause them to follow him and not turn away from him (Deut 30:6; Jer 31:31-34; 32:39-40; Ezek 36:26-27; John 6:44; 8:36; Acts 16:14; 1 Cor 12:3; Phil 1:29; 2 Thess 2:13-14; Jas 1:18; 1 Pet 1:3, 23; 2 Pet 1:3; 1 John 5:1). God supplies what he demands. We work because God works in us (Phil 2:13). For those who do not believe, God holds them responsible for their sin on the basis of the evil intentions of their heart. They have no desire to please or honor God and are rebels against him (Rom 3:10-19). They are willing slaves to sin who need to be rescued by Christ (John 8:34).