Cosmas Indicopleustes

For on the third day the fruits were produced, and in order again that it might not be supposed that they were produced by the influence of the sun, it was not until their creation was finished, that He made the sun and the moon and the stars. But whence did He make them? For it has been said that on the first day He made all things of nothing, but on the other days, out of things existing. Whence then the Sun? …

The Christian Topography, Book 10 ↗

Bede

God also made two great luminaries. We can understand the great luminaries not so much by comparison with others but by their role, as the heaven is great and the sea is great. For there is also the great sun which fills the world with its heat, or the moon with its light, which, wherever they are in the sky, illuminate all the earth and are equally observed by everyone. An evident example of their greatness is that they appear the same to all people. …

Commentary on Genesis (Hexaemeron) ↗

Bonaventure

GOD made the two great lights, etc. It has been said that contemplation consists in the delicious consideration of the heavenly Monarchy, the delicious consideration of the Church Militant, and the delicious consideration of the hierarchized human mind, or of [that mind] ordained in a hierarchical manner. The first is understood through the sun, the second through the moon, and the third through the stars. We should speak first of the sun. The Eternal Sun, Father, Son, and Holy Spirit, is alive, resplendent and warming. …

Collations on the Hexaemeron, Collation 21 ↗

Victorinus of Pettau

To me, as I meditate and consider in my mind concerning the creation of this world in which we are kept enclosed, even such is the rapidity of that creation; as is contained in the book of Moses, which he wrote about its creation, and which is called Genesis. God produced that entire mass for the adornment of His majesty in six days; on the seventh to which He consecrated it . . . with a blessing. …

On the Creation of the World ↗