Musar for Sanhedrin 21:15

G–d therefore told the moon that the adjective "small" that would be used for the righteous, such as in the case of Jacob, Samuel and David, would serve as assurance that the moon was not considered inferior. By the same token, there is no point in calling someone "small" unless this is in contrast to something else that is called "big. Here, the Jewish people as a whole may be considered "big," for G–d had referred to it as בני בכורי ישראל, "My firstborn son Israel." The three examples of "small" people selected were Jacob, Samuel and David because these three people are also described on occasion as the equivalent of "big". The prophet Samuel is described as שמואל הרמתי, "at home in an elevated place," (similar to Samuel I 8,4). The Talmud describes that Samuel "the small one" [a scholar in the third century] was of such a caliber that, had his personal merits only been the determining factor, the spirit of G–d would have come to rest on him. The prophet Samuel i.e. the "big" Samuel, was ranked equal to Moses in many respects. Taanit 25 relates that the "small" Samuel only had to decree a fast in order to pray for rain when rain would already materialize without the people having commenced their fast even. The fact that David was described on occasion as the "small one," suggests that there must also have been a "big" David. The "big" David will be David when he re-emerges as the Messiah. It is said of him (Psalms 72,8) : וירד מים עד הים ודוד שמו, "Let him rule from sea to sea, etc." The Psalmist means that whereas initially the domain of David would be small, eventually it would encompass the whole globe. The message is that "small" and "big" will combine, i.e. study and performance of Torah commandments together will bring about the ideal state, will make a "big one" out of a formerly "small one." This is different from דבור, words of Torah, which will be graciously received by G–d even if they do not reflect penetration to the deeper meaning of the Torah. In other words, words of Torah do not require to be supported by full understanding, whereas mere study, i.e. listening to someone else's discourse on Torah does. When we view the conversation in this light, we find that G–d certainly had the "last word," i.e. was not "defeated" in this verbal encounter. Nevertheless, when G–d saw that the moon was unhappy although it had been shown that it was wrong, He decided to assuage its feelings since He wants His creatures to be happy and content with the fate assigned to them.