kopa-kalo yugantas te
hato ’yam asuro ’lpakah
tat-sutam pahy upasrtam
bhaktam te bhakta-vatsala
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Lord Siva said: The end of the millennium is the time for Your anger. Now that this insignificant demon Hiranyakasipu has been killed, O my Lord, who are naturally affectionate to Your devotee, kindly protect his son Prahlada Maharaja, who is standing nearby as Your fully surrendered devotee.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The Supreme Personality of Godhead is the creator of the material world. There are three processes in creation — namely creation, maintenance and finally annihilation. During the period of annihilation, at the end of each millennium, the Lord becomes angry, and the part of anger is played by Lord Siva, who is therefore called Rudra. When the Lord appeared in great anger to kill Hiranyakasipu, everyone was extremely afraid of the Lord’s attitude, but Lord Siva, knowing very well that the Lord’s anger is also His lila, was not afraid. Lord Siva knew that he would have to play the part of anger for the Lord. Kala means Lord Siva (Bhairava), and kopa refers to the Lord’s anger. These words, combined together as kopa-kala, refer to the end of each millennium. Actually the Lord is always affectionate toward His devotees, even though He may appear very angry. Because He is avyayatma — because He never falls down — even when angry the Lord is affectionate toward His devotees. Therefore Lord Siva reminded the Lord to act like an affectionate father toward Prahlada Maharaja, who was standing by the Lord’s side as an exalted, fully surrendered devotee.