sa vai yada mahadevo
mene khilam ivatmanam
atha me ’bhihito devas
tapo ’tapyata darunam
nava visva-srjo yusman
yenadav asrjad vibhuh
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
When the chief lord of the universe, Lord Brahma [Svayambhu], having been inspired by My energy, was attempting to create, he thought himself incapable. Therefore I gave him advice, and in accordance with My instructions he underwent extremely difficult austerities. Because of these austerities, the great Lord Brahma was able to create nine personalities, including you, to help him in the functions of creation.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Nothing is possible without tapasya. Lord Brahma, however, was empowered to create this entire universe because of his austerities. The more we engage in austerities, the more we become powerful by the grace of the Lord. Therefore Rsabhadeva advised His sons, tapo divyam putraka yena sattvam suddhyed: “One should engage in penance and austerity to attain the divine position of devotional service. By such activity, one’s heart is purified.” (Bhag. 5.5.1) In our material existence we are impure, and therefore we cannot do anything wonderful, but if we purify our existence by tapasya, we can do wonderful things by the grace of the Lord. Therefore tapasya is very important, as stressed in this verse.