The Blessed Lord said I taught this imperishable Yoga to Vivasvan; he told it to Manu; Manu proclaimed it to Ikshvaku.
In simple words
Krishna reveals to Arjuna that this teaching is ancient: "I first taught this eternal wisdom to Vivasvan, the sun god. Vivasvan passed it to Manu, the father of humanity. Manu passed it to King Ikshvaku. That is how old this teaching is."
4.1 इमम् this? विवस्वते to Vivasvan? योगम् Yoga? प्रोक्तवान् taught? अहम् I? अव्ययम् imperishable? विवस्वान् Vivasvan? मनवे to Manu? प्राह taught? मनुः Manu? इक्ष्वाकवे to Ikshvaku? अब्रवीत् taught.Commentary Vivasvan means the sun. Ikshvaku was the son of Manu. Ikshvaku was the reputed ancestor of the solar dynasty of Kshatriyas.This Yoga is said to be imperishable because the result or fruit? i.e.? Moksha? that can be attained through it is imperishable.If the rulers of dominions possess a knowledge of the Yoga taught by Me in the preceding two discourses? they can protect the Brahmanas and rule their kingdom with justice. So I taught this Yoga to the Sungod in the beginning of evolution.
Contemporary scholarly and practical interpretations for modern seekers.
This interpretation draws on a specific tradition and may not represent the view of any single school. For authoritative guidance within a specific tradition, seek a qualified teacher.
Modern
# BG 4.1
As mentioned in the preamble to this chapter, the Lord here clarifies that the teaching He has imparted thus far is not new, but rather a restatement of the eternal knowledge expounded in the Vedas. Awakened by the remembrance of His own nature, the Lord proclaims that He Himself imparted this knowledge at the beginning of creation to Vivasvan, the solar deity. Vivasvan taught this knowledge to his son Manu, the ancient lawgiver of Bharat. Manu in turn instructed King Ikshvaku, the ancestor of the solar dynasty, whose kings ruled Ayodhya for ages.
The word Veda is derived from the Sanskrit root vid, meaning "to know." Thus Veda signifies knowledge, or the means of knowledge. The subject matter of the Vedas is the understanding of the pure, conscious nature of the individual soul and the means of its manifestation.
Just as we may call electricity eternal, for it existed before its first discovery by us, and will continue to exist even if we forget it—similarly, the imperishable, divine, conscious Self is not destroyed by our ignorance of it. The knowledge of this indestructible atman is truly imperishable.
Modern science too acknowledges that the creation of the universe should begin with the sun. As the source of energy, the sun came into being first, and with its emergence, this supreme knowledge of the Self was given to the world.
Since the subject of the Vedas is direct experience of the atman, words are utterly inadequate to describe it. No profound experience can be fully expressed through language. Therefore, studying the scriptures through one's own intellect alone leads not to true understanding, but rather to the likelihood of misunderstanding. Thus, in Bharat, there has been an ancient tradition that spiritual knowledge is received through the words of a guru established in direct experience of the Self. This knowledge has been transmitted through the guru-disciple lineage. Here, we are introduced to the students of this Brahmavidya from ancient times.