John Gill emphasizes the call to holiness as a reflection of God's nature, explaining that God, who is inherently holy, calls believers not just externally but through the transformative power of His Spirit. This divine calling instills principles of holiness within believers, urging them to live out their faith in all aspects of life. Gill highlights that while internal holiness is God's work, external holiness is the believer's response, mirroring God's character in their daily conduct. The sermon stresses the importance of living a life that is worthy of the calling received, as a demonstration of obedience and reverence to God. Ultimately, believers are encouraged to imitate God's holiness in their interactions with both God and others.