Anxious thought or worry is one. Often worries are over physical things like what we will eat, drink and wear (Matthew 6:25 Matthew 6:25Therefore I say to you, Take no thought for your life, what you shall eat, or what you shall drink; nor yet for your body, what you shall put on. Is not the life more than meat, and the body than raiment?
American King James Version×). Avoid getting bogged down with problems by focusing on our ultimate goal—the Kingdom of God (verses 33-34).
Some studies indicate that only about 8 percent of our worries will ever affect our lives. That means a full 92 percent of our worries are a waste of time. They can sap our energy and destroy our faith. A friend of mine turns her problems over to God by imagining she is serving a volleyball up to God and leaving it there for Him to handle.
Fear is a second enemy of faith. Christ directly connected fear to losing faith. When a storm struck the boat carrying Him and His disciples, He rebuked them for being overly concerned for their safety: "Why are you fearful, O you of little faith?" (Matthew 8:24-26 Matthew 8:24-26  And, behold, there arose a great tempest in the sea, so that the ship was covered with the waves: but he was asleep.
 And his disciples came to him, and awoke him, saying, Lord, save us: we perish.
 And he said to them, Why are you fearful, O you of little faith? Then he arose, and rebuked the winds and the sea; and there was a great calm.
American King James Version×, emphasis added throughout).
The apostle John explained, "There is no fear in love; but perfect love casts out fear, because fear involves torment. But he who fears has not been made perfect in love" (1 John 4:18 1 John 4:18There is no fear in love; but perfect love casts out fear: because fear has torment. He that fears is not made perfect in love.
American King James Version×). Love and fear are mutually exclusive. If we have perfect love we will not fear. But if we have fear we do not have perfect love.
Doubt is another enemy of faith. When Peter was walking on water to meet Christ he began to sink. Christ pointed to the cause of the problem: "O you of little faith, why did you doubt?" (Matthew 14:31-32 Matthew 14:31-32  And immediately Jesus stretched forth his hand, and caught him, and said to him, O you of little faith, why did you doubt?
 And when they were come into the ship, the wind ceased.
American King James Version×).
Human reasoning is one of the biggest enemies of faith. James maps out how this process works: "But let him ask in faith, nothing wavering. For he that wavereth is like a wave of the sea driven with the wind and tossed" (James 1:6 James 1:6But let him ask in faith, nothing wavering. For he that wavers is like a wave of the sea driven with the wind and tossed.
American King James Version×, King James Version).
The Greek word translated "wavering" is diakrino. It means "thorough judgment." It is like going back and forth in our minds trying to judge within ourselves. We are told not to lean to our own understanding (Proverbs 3:5 Proverbs 3:5Trust in the LORD with all your heart; and lean not to your own understanding.
American King James Version×).
Using too much human reasoning can limit our trust in God. Barnes' Notes explains: "In regard to the matter under consideration, there is to be no hesitancy, no doubting, no vacillation of the mind. We are to come to God with the utmost confidence and assurance." UN