Lord Brahmā wanted to point out to the demigods that by the strength of the guru one can become most powerful within this world, and by the displeasure of the guru one can lose everything. This is confirmed by the song of Viśvanātha Cakravartī Ṭhākura:

yasya prasādād bhagavat-prasādo yasyāprasādān na gatiḥ kuto ’pi

“By the mercy of the spiritual master one is benedicted by the mercy of Kṛṣṇa. Without the grace of the spiritual master, one cannot make any advancement.” Although the demons are insignificant in comparison to Lord Brahmā, because of the strength of their guru they were so powerful that they could even seize Brahmaloka from Lord Brahmā. We therefore pray to the spiritual master:

mūkaṁ karoti vācālaṁ paṅguṁ laṅghayate girim yat-kṛpā tam ahaṁ vande śrī-guruṁ dīna-tāraṇam

(Madhya 17.80)

By the mercy of the guru, even a dumb man can become the greatest orator, and even a lame man can cross mountains. As advised by Lord Brahmā, one should remember this śāstric injunction if one desires success in his life.