What are the 5 Principal Subject Matters that have been discussed in Bhagavad-Gītā ?

QA : Verse no. 18.78
Question 1 : What are the five principal subject matters that have been discussed in Bhagavad-gītā ?
Answer 1 : "In Bhagavad-gītā five principal subject matters have been discussed: the Supreme Personality of Godhead, material nature, the living entities, eternal time and all kinds of activities. All of these are dependant on the Supreme Personality of Godhead, Kṛṣṇa. All conceptions of the Absolute Truth, namely, impersonal Brahman, localized Paramātmā, or any other transcendental conception, exist within the category of understanding the Supreme Personality of Godhead. Although superficially the Supreme Personality of Godhead, the living entity, material nature and time appear to be different, nothing is different from the Supreme. But the Supreme is always different from everything. Lord Caitanya’s philosophy is that of "inconceivably one and different." This system of philosophy constitutes perfect knowledge of the Absolute Truth."
Question 2 : What are the three principal realizations of the Absolute Truth ? Which one of them is the most perfect ?
Answer 2 : "Absolute Truth is realized in three features-impersonal Brahman, localized Paramātmā, and the Supreme Personality of Godhead, Kṛṣṇa. Perfect knowledge of the Absolute Truth means perfect knowledge of Kṛṣṇa. If one understands Kṛṣṇa, then all the departments of knowledge are part and parcel of that understanding. Kṛṣṇa is transcendental, for He is always situated in His eternal internal potency."
"From Bhagavad-gītā we can understand that to realize oneself by philosophical speculation and by meditation is one process, but to fully surrender unto Kṛṣṇa is the highest perfection. This is the essence of the teachings of Bhagavad-gītā. The path of regulative principles according to the orders of social life and according to the different courses of religion may be a confidential path of knowledge in as far as the rituals of religion are confidential, but one is still involved with meditation and cultivation of knowledge. Surrender unto Kṛṣṇa in devotional service in full Kṛṣṇa consciousness is the most confidential instruction and is the essence of the Eighteenth Chapter."
Ref : Bhagavad-gita 18.78, Purport, Srila Prabhupada
