As previously explained, the demon was originally a servitor of the Lord in Vaikuntha, but somehow or other he fell as a demon. His fight with the Supreme Lord was meant for his liberation. The Lord enjoyed the striking on His transcendental body, just like a fully grown-up father fighting with his child. Sometimes a father takes pleasure in having a mock fight with his small child, and similarly the Lord felt Hiranyaksas striking on His body to be like flowers offered for worship. In other words, the Lord desired to fight in order to enjoy His transcendental bliss; therefore He enjoyed the attack.