Since Adam sinned in the garden of Eden, sin has been the downfall of man. Sin is defined in the Scriptures as “all unrighteousness” (1 John 3:4) and “whatsoever is not of faith” (Romans 14:23). Also, failure to do what we know we should do is term a sin (James 4:17).
The punishment for sin is death; both physical and spiritual (Romans 6:23, James 1:15, Genesis 2:17, and Ezekiel 18:20). The spiritual death one must suffer is eternal separation from God in the lake of fire (Revelation 20:14, 15).