John Chrysostom

"Then shall the righteous shine forth as the sun in the kingdom of their Father." Not because it will be just so much only, but because this star is surpassed in brightness by none that we know. He uses the comparisons that are known to us.

Homily on the Gospel of Matthew 47 ↗

Theophylact of Ohrid

Since the sun appears brighter to us than all the stars, He compares the radiance of the righteous to the sun. For they will shine more resplendently than the sun. Since, perhaps, Christ is the Sun of Righteousness, so the righteous will shine as Christ Himself, for they, too, will be gods.

Commentary on Matthew ↗

Jerome

Then the righteous will shine like the sun in the kingdom of their Father. Let anyone with ears listen!

Commentary on Matthew ↗

Thomas Aquinas

Then shall the just shine as the sun in the kingdom of their Father. Here he explains as to the good; and in them there will be a twofold splendor, namely, in the soul, by which they will see God; Ps 35:10: in your light we shall see light, namely, uncreated light; Isa 58:11: and he shall fill your soul with brightness. And it will overflow into the body; Phil 3:21: he will reform the body of our lowliness, made like to the body of his glory. Wis 3:7: the just shall shine, and shall run to and fro like sparks among the reeds, etc. …

Commentary on Matthew ↗

Bonaventure

There indeed shall be goods of body and soul, such as eye has not seen, nor ear heard, nor the heart of man conceived. Why then do you wander through many things, O little man, seeking the goods of your soul and your body? Love the one good, in which are all goods, and it suffices. Desire the simple good, which is every good, and it is enough. For what do you love, my flesh, what do you desire, my soul? There is whatever you love, whatever you desire. If beauty delights: the just shall shine as the sun.

Breviloquium, Part 7 ↗