Blow the horn on the new moon: The time at which the moon is renewed like "your new moons and your festivals, Shabbat and Rosh Hodesh" and it is written in the Torah that the trumpets should be blown then and it is appropriate that the shofar should be sounded then too. And our rabbis of blessed memory interpreted this verse to be a reference to Rosh Hashanah.
And the explanation of "ba-kesseh" is that the moon is concealed on that day and that is the rule for every new moon.
"Ba-Kesseh' means a time set aside and designated as in "the day set aside" in Proverbs Chapter 7, and the letter "heh" replaces an "aleph."
שהחדש מתכסה בו הוי אומר זה ר"ה
on which the moon is covered, i.e., hidden? You must say that this is Rosh HaShana, which is the only Festival that occurs at the beginning of a month, when the moon cannot be seen.
רַבָּנָן פָּתְרִין קְרָא בְּרֹאשׁ הַשָּׁנָה וְיוֹם הַכִּפּוּרִים, אוֹרִי בְּרֹאשׁ הַשָּׁנָה וְיִשְׁעִי בְּיוֹם הַכִּפּוּרִים,
וַיַּרְא אֱלֹקִים אֶת כָּל אֲשֶׁר עָשָׂה וגו' (בראשית א, לא), רַבִּי לֵוִי פָּתַח (משלי כה, ב): כְּבֹד אֱלֹקִים הַסְתֵּר דָּבָר וּכְבֹד מְלָכִים חֲקֹר דָּבָר. רַבִּי לֵוִי בְּשֵׁם רַבִּי חָמָא בַּר חֲנִינָא אָמַר, מִתְּחִלַּת הַסֵּפֶר וְעַד כָּאן כְּבֹד אֱלֹקִים הוּא, הַסְתֵּר דָּבָר. מִכָּאן וָאֵילָךְ כְּבֹד מְלָכִים חֲקֹר דָּבָר, כְּבוֹד דִּבְרֵי תוֹרָה שֶׁנִּמְשְׁלוּ בִּמְלָכִים, שֶׁנֶּאֱמַר (משלי ח, טו): בִּי מְלָכִים יִמְלֹכוּ, לַחְקֹר דָּבָר.
"And God saw all that He had done etc." Rabbi Levi interpreted this as follows: "the glory of God is concealment and the honor of kings is investigation." Rabbi Levi in the name of Rabbi Hama bar Hanina said, "from the beginning of the book until now the paradigm is "the honor of God is concealment," from here on the paradigm is "the honor of kings is to investigate." The honor of Torah, since they are compared to kings as it says in Proverbs 8:15, "through me kings shall rule" is through investigation.
