The acts of the flesh are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like.
Galatians 5:19-21
The most common cause of spiritual weakness in a Christian, or a church, is a failure to recognize the flesh in its disguise of religious zeal. Like Peter flashing a sword in Gethsemane, the fleshly Christian thinks he is doing God's will and fighting God's battles for him.
Any works that we perform an believe adds to the finished work of Christ on the cross is selfish ambition. They may seem right in the eyes of man but salvation is by faith alone, not by faith plus works