Bhagavad Gita 13.1अर्जुन उवाच प्रकृतिं पुरुषं चैव क्षेत्रं क्षेत्रज्ञमेव च।एतद्वेदितुमिच्छामि ज्ञानं ज्ञेयं च केशव ॥

In some of the books you will not find this verse. If you include this verse also, the number of verses of the Bhagavad Gita will come to 701. Some commentators look upon this verse as an interpolation.We have come to the beginning of the third section of the Gita. Essentially the same knowledge is taught in this section but there are more details.This discourse on Kshetra (matter) is commenced with a view to determine the essential nature of the possessor of the two Prakritis (Natures), the lower and the higher, described in chapter VII, verses 4 and 5.In the previous discourse a description of the devotee who is dear to the Lord is given from verse 13 to the end. Now the question arises What sort of knowledge of Truth should he possess The answer is given in this discourse.Nature is composed of the three alities. It transforms itself into the body, senses and the sensual objects to serve the two purposes of the individual soul, viz., Bhoga (enjoyment) and Apavarga (liberation).The Gita is divided into three sections illustrative of the three words of the Mahavakya or Great Sentence of the Sama Veda -- TatTvamAsi (That thou art). In accordance with this view the first six chapters deal with the path of action or Karma Yoga and the nature of the thou (TvamPada). The next six chapters explain the path of devotion or Bhakti Yoga and the nature of That (TatPada)