But it is monstrous and unlawful to compare God the Father, in the generation of His only-begotten Son, and in the substance of the same, to any man or other living thing engaged in such an act; for we must of necessity hold that there is something exceptional and worthy of God which does not admit of any comparison at all, not merely in things, but which cannot even be conceived by thought or discovered by perception, so that a human mind should be able to apprehend how the unbegotten God is made the Father of the only-begotten Son. Because His generation is as eternal and everlasting as the brilliancy which is produced from the sun. For it is not by receiving the breath of life that He is made a Son, by any outward act, but by His own nature.
Origen
On First Principles, Book I
Chapter II