13.1 प्रकृतिम् the Prakriti (matter), पुरुषम् the Purusha (Spirit or Soul), च and, एव even, क्षेत्रम् the field, क्षेत्रज्ञम् the knower of the field, एव even, च and, एतत् this, वेदितुम् to know, इच्छामि (I) wish, ज्ञानम् knowledge, ज्ञेयम् what ought to be known, च and, केशव O Kesava.Commentary: 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 estion 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). The last six chapters treat of the path of knowledge or Jnana Yoga and the nature of the middle term art (AsiPada) which establishes the identity of the individual and the Supreme Soul (Jiva Brahma Aikyam).Arjuna now wishes to know in detail the difference between Prakriti and Purusha (Matter and Spirit). He desires to have a discriminative knowledge of the difference between them.