Paul warns us about doctrine and our sinful nature. God intends to fulfill all his promises and all his warnings. Paul weeps while he warns because he has a heart for the lost, just as Jesus does. We must be on guard for those who call themselves Christians but do not live as they should - a wolf in sheep's clothing is dangerous in the example they will be to others. Christ alone saves but we are not to be saved just to continue living sinfully. Jesus didn't come to just forgive us but to also deliver us from sin.