What is Sin?
Let no one say when he is tempted, "I am being tempted by God"; for God cannot be tempted by evil and He tempts no one. But each one is tempted when he dwells on sin and is carried away and enticed by his own lust. Then, when lust has conceived, it gives birth to sin; and when sin is accomplished, it brings forth death (James 1:13-15).
The above is the process by which sin is conceived in the human mind. If we never dwelled on sin, sin would never be conceived in our minds. Dwelling on wrong thoughts -or sin- results in wrong actions. Does that mean Jesus never had wrong thoughts go through His mind? No, of course it doesn't! But He never dwelled on them, so He never carried any of them out (Heb. 5:8-9; Is. 7:14-16).
The tempter is Satan. Those who are tempted are humans (1 Thess. 3:5). We tempt ourselves and Satan also tempts us, just as he tempted our perfect example, Jesus Christ (Luke 4:1-2).
Dwelling on what is wrong is sin because what you dwell on becomes the desire of your heart. Jesus Christ said that if you dwell on adultery, you have already committed it in your heart (Matt. 5:28). A premeditated murder is dwelt upon and planned. Our Creator instructs us to dwell only upon what is good, so we will always say and do things that are good and pleasing to the Lord (Phil. 4:8-9).
Our Father wants us to overcome our evil natures by doing good every moment of every day (Rom. 12:21; 2 Cor. 10:5). Who can stop you from only thinking good thoughts, from only saying good things and from only doing good things? Your old nature will try to stop you. Satan will try to tempt you.
But who is there to harm you if you prove zealous for what is good (1 Peter. 3:13)? No one! So dwell not on evil and sin not. Dwell only on good and do only good for God! Then you will not carry out the desires of the flesh (Gal. 5:16).