dorbhyam brahma-varena ca
vase sa-palaḻ lokams trin
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The elder child, Hiranyakasipu, was unafraid of death from anyone within the three worlds because he received a benediction from Lord Brahma. He was proud and puffed up due to this benediction and was able to bring all three planetary systems under his control.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
As will be revealed in later chapters, Hiranyakasipu underwent severe austerity and penance to satisfy Brahma and thus receive a benediction of immortality. Actually, it is impossible even for Lord Brahma to give anyone the benediction of becoming immortal, but indirectly Hiranyakasipu received the benediction that no one within this material world would be able to kill him. In other words, because he originally came from the abode of Vaikuntha, he was not to be killed by anyone within this material world. The Lord desired to appear Himself to kill him. One may be very proud of his material advancement in knowledge, but he cannot be immune to the four principles of material existence, namely birth, death, old age and disease. It was the Lord’s plan to teach people that even Hiranyakasipu, who was so powerful and strongly built, could not live more than his destined duration of life. One may become as strong and puffed up as Hiranyakasipu and bring under his control all the three worlds, but there is no possibility of continuing life eternally or keeping the conquered booty forever. So many emperors have ascended to power, and they are now lost in oblivion; that is the history of the world.