Being double-minded is not good because such a person is mixed up inside. Sometimes they are spiritual, othertimes they are carnal. Sometimes they trust, othertimes they doubt. Instead of being double-minded the committed Christian should desire a pure heart. A person with a pure heart is totally in love with God. And because they are full of love for the Lord, there is no room within them for fear, doubt, or disobedience. Jesus promised, "Blessed are the pure in heart, for they shall see God (Matthew 5:8)."
Watch out for the symptoms of double-mindedness. Seek to have a pure heart fully devoted to the Lord.