In the beginning of creation there was only Lord Brahmā’s creation.Then the whole planetary system was to be populated. Therefore Brahmā created the seven ṛṣis, Kumāras, Rudras etc. In this way the whole universe is populated by prajāpati. Prajā means generation. Pati means master, husband. Prajāpatis means directly expanding. When Kumāras, the sons of Brahma were also offered to become prajāpati they refused their father’s request by saying “We are not going to marry and beget children.” Since Brahmā was angry, from his anger Lord Śiva or Rudra was generated from his eyes. In higher circle the generation can be produced from any part of the body. But we cannot understand. We simply know one part where from the generation comes. Just like many living entities came out from Brahmā’s nostril, eyes, ear. Even Lord Brahmā himself came out from the navel of Viṣṇu. This requires specific power. Not that we have got some stereotyped ideas. Therefore we sometimes find difficulty to understand the description of the Vedas and the Purāṇas. They do not believe. As soon as we say that there was a lotus flower sprouted from the navel of Lord Viṣṇu, and on that lotus flower Brahmā generated, they call it a story. No. These are not stories. These are fact. But our philosophy is Dr. Frog’s philosophy — “I can simply understand three feet water in the well. That’s all. If there is beyond that well, description of Atlantic Ocean, it is beyond my conception. I therefore refuse.” We have got a tiny brain, which cannot accommodate so many big things. Therefore we disbelieve. This is nāstika. But every description in the Vedic literature, they are fact. That is called āstikyam, to have staunch faith.
Ref >> Srila Prabhupada Vani.