Ephesians 2:3:  Among whom also we all had our conversation in times past in the lusts of our flesh, fulfilling the desires of the flesh and of the mind; and were by nature the children of wrath, even as others.

The Apostle Paul is considered one of the greatest missionaries of the Christian Church.  He lived an exemplary life.  However, Paul is admitting in this passage of Holy Scriptures that not only all people, but he himself has sinful thoughts and desires.  He allowed his mind to dwell on the desires of the flesh; which is a sin against Heavenly Father.

This admission illuminates an important characteristic of this Bible Gem; namely that man can sin against Heavenly Father with his thoughts.  A thought held in the mind and not acted upon is a sin if it expresses a desire that is against one of God's commands.  Not just lust, but also discontent, unrighteous anger, hate, envy, jealousy, and bitterness are sins committed in the mind and in the heart.  While these thoughts control us we are in open rebellion again Heavenly Father, acting as children of wrath.