Text 19
sa mām acintayad devaḥ
praśna-pāra-titīrṣayā
tasyāhaṁ haṁsa-rūpeṇa
sakāśam agamaṁ tadā
saḥ — he (Lord Brahmā); mām — Me; acintayat — remembered; devaḥ — the original demigod; praśna — of the question; pāra — the end, conclusion (the answer); titīrṣayā — with a desire to attain, understand; tasya — unto him; aham — I; haṁsa-rūpeṇa — in My form of Haṁsa; sakāśam — visible; agamam — became; tadā — at that time.
Lord Brahmā desired to attain the answer to the question that was puzzling him, and thus he fixed his mind on Me, the Supreme Lord. At that time, in My form of Haṁsa, I became visible to Lord Brahmā.
Haṁsa means “swan,” and the specific ability of the swan is to separate a mixture of milk and water, extracting the rich, milky portion. Similarly, Lord Kṛṣṇa appeared as Haṁsa, or the swan, in order to separate the pure consciousness of Lord Brahmā from the modes of material nature.