Sin is anything that goes against God’s will and His laws. To commit sin is to transgress or disobey these laws. The lust to sin dwells in human nature. In other words, it is contaminated and motivated by the sinful tendencies that dwell in all people as a result of the fall into sin and disobedience in the garden of Eden. This is the body of sin that we have all since inherited and are born with. The Bible also calls these sinful tendencies the “lusts of the flesh.” This means that as human beings we are tempted by sinful desires and thoughts from our own flesh. John writes that we all “have sin,” but you are not guilty of committing sin unless you first consciously agree to the lusts. Sin can be “put to death” bit by bit by denying the lusts as they become conscious for you. This process was first carried out in Jesus while He Himself was a human being on earth. (1 John 1:8; Romans 6:6; Romans 7:18; Romans 8:3-4)
The “flesh” is all of the sinful desires/temptations/lusts, etc. that dwell in human nature. It is the source of temptation, and nothing good dwells there. (Galatians 5:19-21; Romans 7:18; Galatians 5:24; Romans 8:5)
The term “flesh” can also refer to humankind, or our physical bodies, especially in Old Testament contexts. (Genesis 6:13; Psalm 56:4; 1 Peter 1:24; Ephesians 5:29)