God is merciful. He forgives us for all our past sins. However, after seeking His shelter, if we continue to knowingly sin then we must endure the consequences. Only one who has no devotion in his heart sins purposefully. He never seeks refuge in God, nor does he believe in the power of God, and so he just continues sinning. A devotee would instantly feel guilt upon committing even the smallest mistake. He is God-fearing and so he repents for his misdeeds by dandvats, prayer, penance, etc. Through this he purifies himself. The non-devotee eventually suffers for his ignorance.