John Nelson Darby addresses the importance of true grace versus false pretensions in the church, warning against the dangers of self-confidence masked as humility. He emphasizes that authority in the church comes solely from the Holy Spirit and not from human traditions or arrangements, urging believers to rely on God's truth rather than man-made doctrines. Darby encourages his brother to stand firm in faith and to engage in spiritual battles, asserting that the church must remain subject to the truth of God's Word. He highlights the necessity of maintaining a direct relationship with God, free from interposed authority that could lead to sin. Ultimately, he reassures that God will preserve the essential truths of the faith among His elect until the end.