10 There are inquirers into nature who with a great display of words give reasons for the immobility of the earth. Placed, they say, in the middle of the universe and not being able to incline more to one side than the other because its centre is everywhere the same distance from the surface, it necessarily rests upon itself; since a weight which is everywhere equal cannot lean to either side. It is not, they go on, without reason or by chance that the earth occupies the centre of the universe.
It is its natural and necessary position. As the celestial body occupies the higher extremity of space all heavy bodies, they argue, that we may suppose to have fallen from these high regions, will be carried from all directions to the centre, and the point towards which the parts are tending will evidently be the one to which the whole mass will be thrust together. If stones, wood, all terrestrial bodies, fall from above downwards, this must be the proper and natural place of the whole earth.
If, on the contrary, a light body is separated from the centre, it is evident that it will ascend towards the higher regions. Thus heavy bodies move from the top to the bottom, and following this reasoning, the bottom is none other than the centre of the world. Do not then be surprised that the world never falls: it occupies the centre of the universe, its natural place. By necessity it is obliged to remain in its place, unless a movement contrary to nature should displace it. If there is anything in this system which might appear probable to you, keep your admiration for the source of such perfect order, for the wisdom of God.
Grand phenomena do not strike us the less when we have discovered something of their wonderful mechanism. Is it otherwise here? At all events let us prefer the simplicity of faith to the demonstrations of reason.
Source: Nine Homilies of Hexaemeron (New Advent)