For it is not possible that all those qualities serving that...

For it is not possible that all those qualities serving that purpose be collected in that thing by chance alone. For instance, if a man sees a stone on the ground in a shape fit for sitting, and finds its proportions and fashion of the same kind, then he would come to know that it was made by a maker, and that he had made it and placed it there.

But when he sees nothing in it which may have made it fit for sitting then he becomes certain that its existence in the place was by chance only, without its being fashioned by any maker. Such is also the case with the whole of the universe.

For when a man sees the sun, the moon, and all the stars, which are the cause of the four seasons; of days and nights, of rain, water and winds, of the inhabitation of the parts of the earth, of the existence of man, and of the being of all the animals and the plants and of the earth being fit for the habitation of a man, and other animals living in it; and the water fit for the animals living in it; and the air fit for birds, and if there be anything amiss in this creation and edifice, the whole world would come to confusion and disorder, then he would come to know with certainty that it is not possible that this harmony in it for the different members of the universe -- man, animals, and plants -- be found by chance only.

He will know that there is one who determined it, and so one who made it by intention, and that is God, exalted and magnified may He be. He would know with certainty that the universe is a created thing, for he would necessarily think that it is not possible that in it should be found all this harmony, if it be not made by someone, and had come into existence by chance alone. This kind of argument, is quite definite and at the same time clear, and some have mentioned it here.

It is based upon two principles which are acknowledged by all. One of them being, that the universe, with all its component parts, is found fit for the existence of man and things; secondly, that which is found suitable in all its parts, for a single purpose, leading to a single goal, is necessarily a created thing. So those two principles lead us naturally to admit that the universe is a created thing, and that there is a maker of it.

Hence "the argument of analogy" leads to two things at one and the same time, and that is why it is the best argument for proving the existence of God.