James maintained that the double-minded man would not have his prayers answered because he

James, in his epistle, said that a double-minded man would not have his prayers answered because he is unstable in all his ways. This means that such a person is indecisive, lacking firmness and consistency, and his thoughts and actions are constantly shifting. He is unable to fully trust in God and His promises, and as a result, his prayers lack faith and conviction. Therefore, James advises Christians to have a single-minded devotion to God, being fully committed to Him in both their thoughts and actions, and trusting Him completely in all their endeavors.