Srimad Bhagavadgita Sadhaka Sanjivani -Swami Ramsukhdas
In response to his question Lord Krsna, explained devotion and devotees, in the twelfth chapter, while worship of the Imperishable and the Unmanifested, in the thirteenth and the fourteenth chapters. In the twenty-first verse of the fourteenth chapter, Arjuna asked,"What are the marks of him, who has transcended the three modes of nature? What is his conduct and how does he get, beyond the three modes?" So the Lord explained the marks and conduct of such a transcendental person, and also explained, exclusive devotion, as the means to attain that state. - The Lord, started the fifteenth chapter, in connection with His exclusive devotion. At the end of the chapter, He declared that a person who knows Him, as the Supreme Person worships Him, with his whole being (heart or spirit). He means that persons of divine nature, worship Him. It connotes, that persons of demoniac nature, do not worship Him. Before this chapter also, in the fifteenth verse of the seventh chapter and in the twelfth verse of the ninth chapter, demoniac nature, while in the thirteenth verse of the ninth chapter, divine nature have been described, in brief. So the Lord, started the sixteenth chapter, to explain divine nature and demoniac nature in detail and explicitly.