(Genesis 1:16) "And God made the two great lights." After He called them great, He goes back and calls one of them "the lesser light." This was only because it entered the boundary of its fellow. In all the sacrifices it is written, "one goat for a sin offering," but concerning the new moon it is written, "for a sin offering to the LORD" (Numbers 28:15). The Holy One, blessed be He, said: I caused it to enter the boundary of its fellow. And if this one, which entered by permission, was so diminished by the Holy One, blessed be He, then one who enters without permission, how much more so will he be punished.
How the Moon Was Called Great and Then Called Small
Yalkut Shimoni on Torah 8:9
(בראשית א טז) וַיַּעַש אֱלֹהִים אֶת שְׁנֵי הַמְּאֹרֹת הַגְּדֹלִים. וּמֵאַחַר שֶׁקָּרָא אוֹתָן גְּדוֹלִים חוֹזֵר וְקוֹרֵא אֶת הַמָּאוֹר הַקָּטֹן אֶלָּא עַל יְדֵי שְׁנִּכְנַס בִּתְחוּמוֹ שֶׁל חֲבֵרוֹ. בְּכָל הַקָּרְבָּנוֹת כְּתִיב "שְעִיר עִזִּים אֶחָד לְחַטָּאת", וּבְרֹאשׁ חֹדֶשׁ כְּתִיב (במדבר כח, טו) "לְחַטָּאת לַה'", אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא אֲנִי גָּרַמְתִּי לוֹ לִכָּנֵס בִּתְחוּמוֹ שֶׁל חֲבֵרוֹ. וּמָה אִם זֶה שֶׁנִּכְנַס בִּרְשׁוּת כָּךְ פְּגָמוֹ הַקָּדוֹשׁ בָּרוּךְ הוּא, הַנִּכְנָס שֶׁלֹּא בִּרְשׁוּת עַל אַחַת כַּמָּה וְכַמָּה.