In the Bhagavad Gita - Text and Commentary by Sri Sivananda (Sivananda Press Durban SA) the discourse (summary) is as follows:
This discourse is entitled "Purushottama Yoga " or the "Yoga of the Supreme Person". Here Lord Krishna tells us about the ultimate source of this visible phenomenal universe from which all things have come into being, just like a great tree with all its roots, trunk, branches, twigs, leaves, flowers and fruits which spring forth from the earth, which itself supports thetree and in which it is rooted. Lord Krishna declares that the Supreme Being is the source of all existence, and refers allegorically to this phenomenal universe as being like an inverted tree whose roots are in Para Brahman, and whose spreading branches and foliage constitute all the things and factors that go to make up this vast and variegated created phenomena. This is a very mysterious "Tree" which is very difficult to understand, being a product of His inscrutable power of Maya, and hence a marvellous apparent appearance without having actual reality. One who fully understands the nature of this Samsara-Tree goes beyond Maya. To be attached to it is to be caught in it. The surest way of "cutting down" (transcending) this Samsara is by the excellent weapon of non-attachment and dispassion.
In verses four and five of this discourse the Lord tells us how one goes beyond this visible Samsara and attains the supreme, imperishable status, attaining which one does not have to return to this mortal world of pain and death.
Lord Krishna also describes for us the wonderful mystery of His Presence in this universe and the supreme place He occupies in sustaining everything here. The Lord declares that it is a part of Himself that manifests here as ans individual soul in each body. He Himself is the indwelling Oversoul beyond the self. He is the effulgence inherent in the sun, moon and fire. He is present as the nourishing element in the earth. He is the inner Witness of all beings. He is the supreme Knower even beyond the Vedic knowledge. He is the resplendent Person who is beyond both this perishable material creations as well as the imperishable individual soul which is a part of His eternal essence. Thus, because He is beyond perishable matter and superior to the imperishable soul (enveloped in Maya), He is known in this world as well as in the Vedas as the Supreme Person.
15.1 - sri-bhagavan uvaca urdva-mulam adhah-sakhamashvattham prahur avyayamchandamsi yasya parnaniyas tam veda sa veda-vit - "The Supreme Personality of Godhead said: It is said that there is an imperishable banyan tree that has its roots upward and its branches down and whose leaves are the Vedic hymns. One who knows this tree is the knower of the Vedas."
15.2 - adhas cordhvam prasrtas tasya sakhaguna-pravrddha visaya-pravalahadhas ca mulany anusantatanikarmanubandhini manushya-loke
"The branches of this tree extend downward and upward, nourished by the three modes of material nature. The twigs are the objects of the senses. This tree also has roots going down, and these are bound to the fruitive actions of human society."
15.3 - 4 - na rupam asyeha tathopalabhyatenanto na cadir na ca sampratishthaashvattham enam su-virudha-mulamasanga-sastrena drdhena chittva
tatah padam tat parimargitavyamyasmin gata na nivartanti bhuyahtam eva cadyam purusham prapadyeyatah pravrttih prasrta purani
"The real form of this tree cannot be perceived in this world. No one can understand where it ends, where it begins, or where its foundation is. But with determination one must cut down this strongly rooted tree with the weapon of detachment. Thereafter, one must seek that place from which, having gone, one never returns, and there surrender to that Supreme Personality of Godhead from whom everything began and from whom everything has extended since time immemorial."
15.5 - -moha jita-sanga-dosaadhyatma-nitya vinivrtta-kamahdvandvair vimuktah sukha-duhkha-samjnairgacchanty amudhah padam avyayam tat - "Those who are free from false prestige, illusion and false association, who understand the eternal, who are done with material lust, who are freed from the dualities of happiness and distress, and who, unbewildered, know how to surrender unto the Supreme Person attain to that eternal kingdom."
15.6 - na tad bhasayate suryona sasanko na pavakahyad gatva na nivartantetad dhama paramam mama - "That supreme abode of Mine is not illumined by the sun or moon, nor by fire or electricity. Those who reach it never return to this material world."
15.7 - mamaivamso jiva-lokejiva-bhutah sanatanahmanah-sasthanindriyaniprakriti-sthani karshati - "The living entities in this conditioned world are My eternal fragmental parts. Due to conditioned life, they are struggling very hard with the six senses, which include the mind."
15.8 - sariram yad avapnotiyac capy utkramatishvarahgrhitvaitani samyativayur gandhan ivasayat - "The living entity in the material world carries his different conceptions of life from one body to another as the air carries aromas. Thus he takes one kind of body and again quits it to take another."
15.9 - srotram caksuh sparshanam carasanam ghranam eva caadhisthaya manas cayamvisayan upasevate - "The living entity, thus taking another gross body, obtains a certain type of ear, eye, tongue, nose and sense of touch, which are grouped about the mind. He thus enjoys a particular set of sense objects."
15.10 - utkramantam sthitam vapibhunjanam va gunanvitamvimudha nanupasyantipasyanti jnana-caksusah - "The foolish cannot understand how a living entity can quit his body, nor can they understand what sort of body he enjoys under the spell of the modes of nature. But one whose eyes are trained in knowledge can see all this."
Click here for the remaining verses to this chapter 15.