यद्यप्यस्त्रं ब्रह्मशिरस् त्वमोघं चाप्रतिक्रियम् ।
वैष्णवं तेज आसाद्य समशाम्यद्भृगूद्वह ॥ १५ ॥
yadyapy astram brahma-siras
yadyapi-although; astram-weapons; brahma-Brahma; sirah-supreme; tu-but; amogham-without check; ca-and; apratikriyam-not to be counteracted; vaisnavam-in relation with Visnu; tejah-strength; asadya-being confronted with; samasamyat-was neutralized; bhrgudvaha-O glory of the family of Bhrgu.
O Saunaka, although the supreme brahmastra weapon released by Asvatthama was irresistible and without check or counteraction, when confronted by the strength of Visnu [Lord Krsna], it was neutralized and foiled.
In the Bhagavad-gita it is said that the brahmajyoti or the glowing effulgence transcendental is resting on Lord Sri Krsna. In other words, the glowing effulgence known as brahmatejas is nothing but the rays of the Lord, just as the sun rays are rays of the sun disc. So this Brahma weapon also, although materially irresistible, could not surpass the supreme strength of the Lord. The weapon called brahmasiras, released by Asvatthama, was neutralized and foiled by Lord Sri Krsna by His own energy; that is to say. He did not wait for any other's help because He is absolute.