"Knowing the truth" , in whose opinion ?
As such questions have been exhaustively examined, I would suggest an excellent place to start are the Vedanta Sutras of the great sage Vyasa. For example the first verse says
athato brahma jijnasa
This translates into English as
Now is the time to inquire about the Absolute Truth
So here at the very beginning Vyasa makes it clear what he means to discuss. There are so many forms of life, and they are all associated with a various types of intelligence. However, the human form of life is very special in that it has been endowed with the type of intelligence that makes such inquires possible. Dogs and cats do not have such discussions. But a human being should ask questions like who am I, where have I come from, and what is the purpose of life. Indeed this is what distinguishes the human species from other animals. The Absolute Truth is denoted in this passage by the Sanskrit term Brahman.
Now various Vedic scholars have commented on the Vedanta Sutras, but the great Ramanuja in his commentary on this verse has stated
The word 'Brahman' denotes the hightest Person (purushottama), who is essentially free from all imperfections and possesses numberless classes of auspicious qualities of unsurpassable excellence. The term 'Brahman' is applied to any things which possess the quality of greatness (brihattva, from the root 'brih'); but primarily denotes that which possesses greatness, of essential nature as well as of qualities, in unlimited fullness; and such is only the Lord of all. Hence the word 'Brahman' primarily denotes him alone, and in a secondary derivative sense only those things which possess some small part of the Lord's qualities; for it would be improper to assume several meanings for the word (so that it would denote primarily or directly more than one thing). The case is analogous to that of the term 'bhagavat 1.' The Lord only is enquired into, for the sake of immortality, by all those who are afflicted with the triad of pain. Hence the Lord of all is that Brahman which, according to the Sûtra, constitutes the object of enquiry.
Here Srila Ramanuja Acharya makes it very clear, that Brahman refers to the Supreme Person, or God, who is free from imperfection and possesses the all knowledge, all wealth, all fame, all beauty, all power, and all renunciation.
The second verse goes
janmady asya yatah
Translated into English
That from which everything is coming
The word "janmadi" means the origin, "asya" means everything, and "yatah" means from which. So having established in the first verse the object of inquiry, Vyasa states that the Absolute Truth, Brahman, the Supreme Person, God is that from whom everything is coming.
Again to quote the great Ramanuja
The expression 'the origin', &c., means 'creation, subsistence, and reabsorption'. The 'this' (in 'of this') denotes this entire world with its manifold wonderful arrangements, not to be fathomed by thought, and comprising within itself the aggregate of living souls from Brahmâ down to blades of grass, all of which experience the fruits (of their former actions) in definite places and at definite times. 'That from which,' i.e. that highest Person who is the ruler of all; whose nature is antagonistic to all evil; whose purposes come true; who possesses infinite auspicious qualities, such as knowledge, blessedness, and so on; who is omniscient, omnipotent, supremely merciful; from whom the creation, subsistence, and reabsorption of this world proceed--he is Brahman: such is the meaning of the Sûtra.
So that's a start.