T. Austin-Sparks emphasizes that God's means of achieving His purpose in believers is through the Spirit of sonship and the Cross. He explains that true relationship with God begins with the cry of 'Father' and that the Spirit must work within us to form Christ. Sparks reassures that our spiritual struggles do not hinder God's work, as it is ultimately Christ who energizes us toward God's end. He encourages believers to trust in God's faithfulness, especially during 'off' times when prayer feels difficult, reminding us that it is not our efforts but His grace that sustains us. The key to spiritual life and prayer is a profound faith in Christ, who is always at work within us.