PURPORT

In this regard, Srila Visvanatha Cakravarti Thakura says that although Hiranyakasipu was already purified, he had to take birth on a higher planetary system to become a devotee again. Prahlada Maharaja was advised to perform the ritualistic ceremony as a matter of etiquette, for the Supreme Personality of Godhead under no circumstances wants to stop the regulative principles. Madhva Muni also instructs:

madhu-kaitabhau bhakty-abhava
durau bhagavato mrtau
tama eva kramad aptau
bhaktya ced yo harim yayau

When the demons Madhu and Kaitabha were killed by the Supreme Personality of Godhead, their kinsmen also observed the ritualistic ceremonies so that these demons could return home, back to Godhead.