8. To enable the real meaning of these words to be reached it is also necessary to pay attention to the significance of the word water which is not used here in its usual sense.
The knowledge of physics was very imperfect in ancient times when it was believed that the Earth had risen out of the water. Therefore water was considered to be the exclusive primitive generating substance. This is why we read in the book of Genesis: '...the Spirit of God moved upon the face of the waters; it floated above the waters; .. . Let there be firmament in the midst of the waters; ... Let the waters under the heaven be gathered together unto one place, and let the dry land appear; ... Let the waters bring forth abundantly the moving creature that hath life, and fowl that may fly above the Earth in the open firmament of heaven.'
According then to this belief, water represented the nature of matter, just as the Spirit represented the nature of intelligence. The words: 'If man is not reborn of the waters and of the Spirit, or in water and in Spirit', thus signify -'if man is not born with his body and his soul'. This is the manner in which these words were originally understood.
This interpretation is wholly justified by these other words: What is born of the flesh is flesh and what is born of Spirit is Spirit. Here Jesus established a clear distinction between body and Spirit. What is born of the flesh clearly indicates that only the body generates from the body and that the Spirit is independent.