What he is just at noon, that is the udgîtha. On it the Devas are dependent (because they are brilliant). Therefore they are the best of all the descendants of Pragâpati, for they share the udgîtha of that Sâman.

In plain words: The sun at noon is the main sung part of the chant, and the Devas, the shining gods, belong to it. That is why they are the best of all the children of Pragâpati, the creator.