John Nelson Darby expounds on Mark 4, focusing on the parable of the sower and the various responses to God's word. He emphasizes that true fruitfulness comes from a heart genuinely receptive to God's grace, contrasting it with those who superficially receive the word but fail to endure trials. The sermon illustrates how the kingdom of God grows mysteriously and powerfully, even when it seems hidden, and reassures believers that they are secure with Christ amidst life's storms. Darby highlights the importance of self-judgment and the necessity of allowing God's light to shine through us to bless others.