"Brother B, it is dangerous for you to yield to doubts. You must not permit yourself to go any further in the direction in which you have been going. You are in constant danger. Satan is on your track, suggesting doubts and causing unbelief. Had you stood clear in the counsel of God you could have had an influence for good over those who love your society now. 2T 223.1"
"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."
Both passages address the danger of doubt and its negative consequences. James 1:6 describes the instability caused by wavering faith, while the EGW passage warns against yielding to doubts and unbelief.
Poor Brother C felt the influence of the Spirit of God, but was deficient in experience. He did not fully turn from his old habits. He failed to make God his strength continually, and his feet slipped. There is no concord between Christ and Belial. You might have helped him, had you been connected with Heaven as you should have been. But your course of inactivity, your manner of conversation, your influence, have strengthened him in his backsliding and quieted the voice of conscience within him. Your course has not been a reproof to him in his downward track. You could do good, were you living for God. Your strength is utter weakness, your wisdom foolishness; but you do not realize it. You have been too well satisfied with a theory, a correct form of doctrine, but have not felt the necessity of the power of God; you have neglected the spiritual part of religion. Your whole being should cry out for the Spirit of God—the life and power of religion in the soul, which would lead to the cru…
"Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? and what communion hath light with darkness?"
The phrase "no concord between Christ and Belial" is a direct reference to the principle of separation from unrighteousness found in 2 Corinthians 6:14. The passage expands on this principle in the context of spiritual experience.