John Nelson Darby discusses the significance of Numbers 15, emphasizing God's unwavering purpose despite Israel's rebellion and unbelief. He highlights how, even after the people's failures, God reassures them of their future in the promised land, demonstrating His grace and steadfastness. The chapter outlines the offerings to be made in the land, symbolizing worship and communion with God, and emphasizes the importance of joy and fellowship in worship. Darby also notes the provision for sin, illustrating God's grace in maintaining a relationship with His people despite their shortcomings. Ultimately, he concludes with the assurance of God's enduring presence and commitment to His people.