Sri Aurobindo translates Prashna Upanishad, First Question, Verses 14-16: “Food is the Eternal Father: for of this came the seed and of the seed is the world of creatures born. They therefore who perform the vow of the Eternal Father produce the twin creature. But theirs is the heaven of the spirit in whom are established askesis and holiness and in whom Truth has her dwelling. Theirs is the heaven of the Spirit, the world all spotless, in whom there is neither crookedness nor lying nor any illusion.”
With the background of the earlier responses, starting with the origin of the created universe with energy and matter, and the creation of the divisions of Time, the process of determining the direction and rebirth of the soul through the processes of birth and death, the sage now focuses on the individual action. The processes of perpetuation of the creation take place at the individual level through the combining of the seed in the body of the woman, which creates children, male and female. The sage has previously distinguished between those who follow the path that leads to this action of perpetuation, the path of the southern solstice, and those who follow the path of seeking the Eternal through tapasya, and spiritual focus, who live the Truth of existence through their Oneness in Knowledge with the Spirit.
Sri Aurobindo, The Upanishads, Prashna Upanishad, pp.297-315