Mundaka Upanishad 1.2

This is the truth: the sacrificial works which they (the poets) saw in the hymns (of the Veda) have been performed in many ways in the Tretâ age. Practise them diligently, ye lovers of truth, this is your path that leads to the world of good works!

When the fire is lighted and the flame flickers, let a man offer his oblations between the two portions of melted butter, as an offering with faith.

If a man's Agnihotra sacrifice is not followed by the new-moon and full-moon sacrifices, by the four-months' sacrifices, and by the harvest sacrifice, if it is unattended by guests, not offered at all, or without the Vaisvadeva ceremony, or not offered according to rule, then it destroys his seven worlds.

Kâlî (black), Karâlî (terrific), Manogavâ (swift as thought), Sulohitâ (very red), Sudhûmravarnâ (purple), Sphulinginî (sparkling), and the brilliant Visvarûtpî (having all forms), all these playing about are called the seven tongues (of fire).

If a man performs his sacred works when these flames are shining, and the oblations follow at the right time, then they lead him as sun-rays to where the one Lord of the Devas dwells.

Come hither, come hither! the brilliant oblations say to him, and carry the sacrificer on the rays of the sun, while they utter pleasant speech and praise him, saying: "This is thy holy Brahma-world (Svarga), gained by thy good works."

But frail, in truth, are those boats, the sacrifices, the eighteen, in which this lower ceremonial has been told. Fools who praise this as the highest good, are subject again and again to old age and death.

Fools dwelling in darkness, wise in their own conceit, and puffed up with vain knowledge, go round and round staggering to and fro, like blind men led by the blind.

Children, when they have long lived in ignorance, consider themselves happy. Because those who depend on their good works are, owing to their passions, improvident, they fall and become miserable when their life (in the world which they had gained by their good works) is finished.

Considering sacrifice and good works as the best, these fools know no higher good, and having enjoyed (their reward) on the height of heaven, gained by good works, they enter again this world or a lower one.

But those who practise penance and faith in the forest, tranquil, wise, and living on alms, depart free from passion through the sun to where that immortal Person dwells whose nature is imperishable.

Let a Brâhmana, after he has examined all these worlds which are gained by works, acquire freedom from all desires. Nothing that is eternal (not made) can be gained by what is not eternal (made). Let him, in order to understand this, take fuel in his hand and approach a Guru who is learned and dwells entirely in Brahman.

To that pupil who has approached him respectfully, whose thoughts are not troubled by any desires, and who has obtained perfect peace, the wise teacher truly told that knowledge of Brahman through which he knows the eternal and true Person.