The son of Dronacarya released brahmastra. It has a very great significance for us because "Srimad-Bhagavatam" was spoken because of this event.

Dronacarya was the only one who possessed this very secret knowledge of brahmastra. When he heard that Parasurama gave away all his wealth to brahmanas he decided to approach him. But he came too late, there was nothing left except Parasurama’s body and weapons. Dronacarya chose weapons. Parasurama taught him how to release and to retract brahmastra, but with one condition: Dronacarya should never release this weapon against ordinary people.

After this Dronacarya became a very powerful warrior even though he was a brahmana. Then he became a military teacher for the sons of Pandu and Dhritarastra. Out of all of them Arjuna was his favorite disciple because of his eagerness to learn. This eagerness and desire to serve is the most appreciated by the guru. Therefore Dronacarya secretly gave the mantra to Arjuna, which could invoke the very powerful energy, but also with the same condition, not to use it against ordinary people.

This is how parampara system works. When Asvatthama saw Arjuna’s effulgence he became envious and insisted his father gave this mantra to him also. Ultimately Dronacarya relented and gave him the mantra with the same condition. But due to the rage of the battle Dronacarya himself forgot this promise to his guru, he used divine weapons against ordinary people. It was one of the reasons why he was killed on the battlefield of Kuruksetra.

Karna once approached Dronacarya with the same request to give him this knowledge, but Dronacarya refused. On the battlefield Krisna insisted that Arjuna should use brahmastra against Karna. It was the only time when Arjuna used brahmastra against Karna.

The whole Vedic culture was based on the science of sound. This science of properly pronouncing sounds is the most subtle science that ever existed, it is called siksa. People who did not pay attention to this science were called mlechas, it means not pronounced properly. Science of the sound is material science, but it is in connection with spiritual science. Vedas teach how to pronounce words properly so that you would develop some power. The subtle sound is behind anything gross which we have, so by creating a certain vibration in akasa you can get whatever you want to achieve. The ultimate goal of this science is how to achieve spiritual perfection, because the only way to get out of this material existence is through sound. Spiritual sound is non-different from the Lord Himself.

Caitanya Mahaprabu reveals the meaning of the Vedic sound in "Siksastaka" prayers. By chanting the Holy name properly you will have sphurti of Krisna Himself.