Three important topics contain in first six chapters, there are:
Jīva-svarupam (true nature of individual being)
Karma-yoga (as the supporting means for self-knowledge)
Purusa-prayatna (individual effort for self-knowledge)
Here in next six chapters, the other set of three topics being discussed:
Īśvara-svarupam (nature God as the total of creation)
Upasana (contemplation as the supporting means for self-knowledge)
Īśvara-anugraḥ (grace of god to attempt self-knowledge)
In the last verse of sixth chapter, Lord Krsna said, "one who contemplates upon me (the Lord), he is the most exalted among the yogīs". This is the verse which sowed the seed for this seventh chapter, where the nature of Īśvara being explained in detail for one to contemplate on the oneness between individual and total. As an individual, no matter if one is a believer of God or not, he/she would acknowledge a more exalted power over human being, which is called total. And this total is the source where everything in this creation comes from. Therefore after knowing the nature of the individual, one should also understand the real nature of the total.
mayyāsaktamanāḥ pārtha yogaṃ yuñjanmadāśrayaḥ |
asaṃśayaṃ samagraṃ māṃ yathā jñāsyasi tacchṛṇu ||7.1||
Śrī Bhagavān said: Pārtha (Arjuna)! With a mind committed to me by taking to yoga, and having surrendered to me, please listen to the way in which you will know me totally, without any doubt.
This introduction verse shows what Lord Krsna will teach in the coming six chapters. The main teaching is the knowledge of Īśvara in totality, including saguna-rūpam (conditioned with form) and nirguna-rūpam (true nature without form). But for knowing that one should commit one's mind only for the moksa pursue mayyāsaktamanāḥ - mind committed to me - Īśvara as the means and also the end. This implies that knowledge of Īśvara is myself alone, which is limitless. Yogaṃ yuñjan - taking up certain sadhana - supporting means are required depend upon the qualification of the students to understand this knowledge. madāśrayaḥ - having surrendered to me, by god's grace alone moksa's pursue will be certain.
jñānaṃ te'haṃ savijñānamidaṃ vakṣyāmyaśeṣataḥ |
yajjñātvā neha bhūyo'nyajjñātavyamavaśiṣyate ||7.2||
I will teach you without any omission, this knowledge, along with immediate knowledge, knowing which there remain nothing else to be known here.
There are two knowledge of Īśvara imparted by Lord Krsna here, one is called jñānam - indirect knowledge, where Īśvara is known in the conditioned form. This is a superficial aspect of god which we known in this transactional world. In here, there is a division between god and devotee, therefore it is called indirect knowledge. Another knowledge is called vijñānam - immediate knowledge, where the nature of god without limiting factor as the immediate knowledge one should own up as oneself alone. With this knowledge, one sees the oneness between god and devotee, just like one sees the nature of wave is no different from the ocean.
Next is glorification of the rareness of this knowledge.
manuṣyāṇāṃ sahasreṣu kaścidyatati siddhaye |
yatatāmapi siddhānāṃ kaścinmāṃ vetti tattvataḥ ||7.3||
Among thousands of people, a rare person makes effort for moksa. Even among those seekers making effort, (only) a rare person comes to know me in reality.
The rareness of vijñānam - immediate knowledge as hard to understand is shown. Where as in the transactional world we are all busy pursuing name and form, therefore very few people have the mind to really enquire into the self. Among those who enquired, not many follow the correct means where this knowledge only can be known through śastra unfolded by the lineage of teaching. And among those who know, how many of them can own up this knowledge as the immediate knowledge?
This verse seems to be very discouraging for a student of vedānta at first, but when Lord Krsna said yatatāmapi siddhānāṃ - they are accomplished people, means those who strive in the right direction, as long as the moksa's journey has begun, one will keep picking up the threads and accomplish one day.
Next, prakriya - model of unfoldment, of Īśvara being the source of the creation is talked about.
bhūmirāpo'nalo vāyuḥ khaṃ mano buddhireva ca |
ahaṅkāra itīyaṃ me bhinnā prakṛtiraṣṭadhā ||7.4||
Earth, water, fire, air, space, mind, intellect and indeed the sense of doership - thus this prakrti of mine is divided in an eight-fold way.
Teaching of Bhagavad Gītā is based on the Upanishad alone. And all Upanishad presented Īśvara as jagad-karanam - creator of the universe. As per our experience, everything in the universe has its cause. Therefore this idea is given as an easier way for us to understand Īśvara. In the creation we know of, involved two-fold cause, one is the raw material cause and another one is the intelligent cause. In the case of pot, clay is the material cause and the pot maker is the intelligent cause. But Mundaka-upanishad said "Brahman alone was there before the creation", pointed out that Brahman is both material and intelligent cause for this universe which doesn't undergo any change during the process of creation. These two principles (para -prakrti and apara-prakrti) put together is called god.
iyaṃ me bhinnā prakṛtiraṣṭadhā - thus this prakrti of mine is divided in an eight-fold way. This is one of the prakriyā (teaching model) adopted to explain about creation. Prakriyā is a particular discussion which is useful for understanding the vision. The intention of using any prakriyā is not to reveal creation but to establish that there is nothing other than Brahman. There are different prakriyā - teaching model used in different Upanishad.