The Vedic knowledge is called sruti; knowledge has to be received by hearing. By hearing only can we have access to either material or spiritual enjoyment
SB Canto 3
When egoism in ignorance is agitated by the sex energy of the Supreme Personality of Godhead, the subtle element sound is manifested, and from sound come the ethereal sky and the sense of hearing.
It appears from this verse that all the objects of our sense gratification are the products of egoism in ignorance. It is understood from this verse that by agitation of the element of egoism in ignorance, the first thing produced was sound, which is the subtle form of ether. It is stated also in the Vedānta-sūtra that sound is the origin of all objects of material possession and that by sound one can also dissolve this material existence. Anāvṛttiḥ śabdāt means "liberation by sound." The entire material manifestation began from sound, and sound can also end material entanglement, if it has a particular potency. The particular sound capable of doing this is the transcendental vibration Hare Kṛṣṇa. Our entanglement in material affairs has begun from material sound. Now we must purify that sound in spiritual understanding. There is sound in the spiritual world also. If we approach that sound, then our spiritual life begins, and the other requirements for spiritual advancement can be supplied. We have to understand very clearly that sound is the beginning of the creation of all material objects for our sense gratification. Similarly, if sound is purified, our spiritual necessities also are produced from sound.
Here it is said that from sound the ether became manifested and that the air became manifested from ether. How the ethereal sky comes from sound, how the air comes from sky and how fire comes from air will be explained later on. Sound is the cause of the sky, and sky is the cause of śrotram, the ear. The ear is the first sense for receiving knowledge. One must give aural reception to any knowledge one wants to receive, either material or spiritual. Therefore śrotram is very important. The Vedic knowledge is called śruti; knowledge has to be received by hearing. By hearing only can we have access to either material or spiritual enjoyment.
In the material world, we manufacture many things for our material comfort simply by hearing. They are already there, but just by hearing, one can transform them. If we want to build a very high skyscraper, this does not mean that we have to create it. The materials for the skyscraper—wood, metal, earth, etc.—are already there, but we make our intimate relationship with those already created material elements by hearing how to utilize them. Modern economic advancement for creation is also a product of hearing, and similarly one can create a favorable field of spiritual activities by hearing from the right source. Arjuna was a gross materialist in the bodily conception of life and was suffering from the bodily concept very acutely. But simply by hearing, Arjuna became a spiritualized, Kṛṣṇa conscious person. Hearing is very important, and that hearing is produced from the sky. By hearing only can we make proper use of that which already exists. The principle of hearing to properly utilize preconceived materials is applicable to spiritual paraphernalia as well. We must hear from the proper spiritual source.