All religious scriptures describe lower planetary systems or hell and higher systems or heaven. A living entity can prepare itself for heaven or hell by the appropriate preparation; as you sow, so shall you reap is the law that governs. Sinful activities can be by thought, word or deed and one has to suffer punishment. People do not believe in the next life because they want to avoid punishment, but one cannot avoid the next life nor save oneself from the laws of nature. We may deny the existence of God and His laws but God and His laws are still there. According to the law of karma if we act properly we are rewarded and if we act sinfully we suffer. Wherever we reach in this life is the starting point in the next life. According to the Vedic way of life, if a person commits a sin and counteracts it by penance, that is atonement; one has to execute the prescribed atonement according to the gravity of the sinful activity. Sinful activities are like diseases and one should follow the prescribed cures to become healthy.