The complete whole, Personality of Godhead, has immense potencies (parāsya śaktir vividhaiva śrūyate (Cc. Madhya 13.65, purport). How Kṛṣṇa is acting in different potencies is also explained in Bhagavad-gītā. This phenomenal world or material world in which we are placed is also complete in itself because the twenty-four elements of which this material universe is a temporary manifestation, according to Sāṅkhya philosophy, are completely adjusted to produce complete resources which are necessary for the maintenance and subsistence of this universe. There is nothing extraneous, nor is there anything needed. This manifestation has its own time fixed by the energy of the supreme whole, and when its time is complete, these temporary manifestations will be annihilated by the complete arrangement of the complete. There is complete facility for the small complete units, namely the living entities, to realize the complete, and all sorts of incompleteness are experienced due to incomplete knowledge of the complete. So Bhagavad-gītā contains the complete knowledge of Vedic wisdom.
All Vedic knowledge is infallible, and Hindus accept Vedic knowledge to be complete and infallible. For example, cow dung is the stool of an animal, and according to smṛti, or Vedic injunction, if one touches the stool of an animal he has to take a bath to purify himself. But in the Vedic scriptures cow dung is considered to be a purifying agent. One might consider this to be contradictory, but it is accepted because it is Vedic injunction, and indeed by accepting this, one will not commit a mistake; subsequently it has been proved by modern science that cow dung contains all antiseptic properties. So Vedic knowledge is complete because it is above all doubts and mistakes, and Bhagavad-gītā is the essence of all Vedic knowledge.
Vedic knowledge is not a question of research. Our research work is imperfect because we are researching things with imperfect senses. We have to accept perfect knowledge which comes down, as is stated in Bhagavad-gītā, by the paramparā (disciplic succession). We have to receive knowledge from the proper source in disciplic succession beginning with the supreme spiritual master, the Lord Himself, and handed down to a succession of spiritual masters. Arjuna, the student who took lessons from Lord Śrī Kṛṣṇa, accepts everything that He says without contradicting Him. One is not allowed to accept one portion of Bhagavad-gītā and not another. No. We must accept Bhagavad-gītā without interpretation, without deletion and without our own whimsical participation in the matter. The Gītā should be taken as the most perfect presentation of Vedic knowledge. Vedic knowledge is received from transcendental sources, and the first words were spoken by the Lord Himself. The words spoken by the Lord are called apauruṣeya, meaning that they are different from words spoken by a person of the mundane world who is infected with four defects. A mundaner (1) is sure to commit mistakes, (2) is invariably illusioned, (3) has the tendency to cheat others and (4) is limited by imperfect senses. With these four imperfections, one cannot deliver perfect information of all-pervading knowledge.