Bhagavad Gita 13.20प्रकृतिं पुरुषं चैव विद्ध्यनादी उभावपि।विकारांश्च गुणांश्चैव विद्धि प्रकृतिसंभवान् ॥

Steps are necessary to reach the top floor of a building. Even so, steps are necessary to reach the summit of the knowledge of the Self. That is the reason why Lord Krishna took Arjuna to the summit of knowledge step by step. He first taught Arjuna the nature of the field, then knowledge, ignorance or nonwisdom, and ultimately the knowable. When a child is to be fed,the intelligent mother divides the food into small portions and feeds the child little by little. Even so Lord Krishna fed His spiritual child Arjuna with the spiritual food little by little.Lord Krishna says O Arjuna I will give you the same teaching in another form by the description of the Spirit and Nature.Till now the Lord expounded the knowledge of the field and the Self in accordance with the philosophy of the Upanishads. Now He explains the same knowledge in accordance with the Sankhya philosophy, but without accepting its dual nature in the form of discrimination between the Spirit and Nature.Vikaras Modifications from the MahatTattva or intellect down to the physical body the twentyfour principles of the Sankhyas. The Self within is changeless. All changes take place in Nature