G. Campbell Morgan emphasizes the significance of 'the day of the Lord' as revealed in Zephaniah, highlighting God's direct and supernatural judgment upon sin, particularly luxury and indifference. He explains that this day contrasts the patience of God with the impending judgment, which will ultimately lead to the establishment of God's Kingdom and a new order characterized by joy and service. Morgan stresses the importance of recognizing our responsibility in light of this assurance, urging believers to live holy lives and remain vigilant as they await the fulfillment of God's promises. The sermon calls for a renewal of passion for God's judgment that brings about restoration and new beginnings.