Further clarification is still necessary:וְצָרִיךְ לְהָבִין,
According to the explanations offered above, the fact that the refinement of the primary emotional attributes was completed on Rosh Chodesh Sivanדִּלְפִי הַנַּ"ל, זֶה שֶׁבְּרֹאשׁ חֹדֶשׁ סִיוָן נִשְׁלְמוּ עִקְּרֵי הַמִּדּוֹת
highlights man’s attainment of shleimus.הוּא בֵּאוּר בִּשְׁלֵמוּת הָאָדָם,
However, the maamar in Torah Or associates this dimension with the fact that the birth of the new moon occurs on Rosh Chodesh,וּבְהַדְּרוּשׁ שֶׁבְּתוֹרָה אוֹר מְקַשֵּׁר זֶה עִם זֶה שֶׁבְּרֹאשׁ חֹדֶשׁ הוּא מוֹלַד הַלְּבָנָה,
underscoring the quality of bittul.עִנְיַן הַבִּטּוּל.
In resolution, it is possible to offer the following explanation:וְיֵשׁ לוֹמַר הַבֵּאוּר בָּזֶה,
The birth of the new moon highlightsדְּעִנְיַן מוֹלַד הַלְּבָנָה הוּא
(not the moon’s bittul, but, on the contrary,)(לֹא הַבִּטּוּל שֶׁלָּהּ, אֶלָּא אַדְּרַבָּה)
the renewal of its existenceשֶׁנּוֹלָד מְצִיאוּתָהּ,
through the light of the sun being drawn to it and subsequently, reflected by it. For Rosh Chodesh is not when the light of the moon is hidden, but when it shines anew.עַל יְדֵי שֶׁנִּמְשָׁךְ בָּהּ אוֹר הַשֶּׁמֶשׁ.
In Chassidus,1 similar concepts are explained in interpretation of the verse,2 “Tomorrow is the new moon, and you will be called to mind, because your seat will be vacant.”
“Your seat will be vacant,” the quality of bittul, represents the Divine service associated with the day preceding Rosh Chodesh, when the moon’s light is not at all visible. Rosh Chodesh, by contrast, represents the Divine service of “you will be called to mind,” the renewal of the moon’s shining.
The fact that the moon is merely a point at the time of its birth,וְזֶה שֶׁבְּעֵת הַמּוֹלָד הִיא רַק נְקֻדָּה בִּלְבָד,
which emphasizes its bittul (as explained above),שֶׁזֶּה מוֹרֶה עַל הַבִּטּוּל שֶׁלָּהּ (כַּנַּ"ל),
highlights that the very existence of the moon,הוּא, שֶׁהַמְּצִיאוּת דְּהַלְּבָנָה,
its light,הָאוֹר שֶׁלָּהּ,
is characterized by bittul;הִיא בִּבְחִינַת בִּטּוּל,
it is perceived that its light is not its own,שֶׁנִּרְגָּשׁ בָּהּ שֶׁהָאוֹר שֶׁבָּהּ הוּא לֹא מִשֶּׁל עַצְמָהּ
but rather solely what it receives and reflects from the sun.וְרַק שֶׁמְּקַבֶּלֶת מֵהַשֶּׁמֶשׁ.
Similar concepts apply to the Jewish people,וְעַל דֶּרֶךְ זֶה הוּא בְּיִשְׂרָאֵל
who establish their calendar according to the moon.שֶׁמּוֹנִין לַלְּבָנָה,
The parallel to the bittul of Rosh Chodesh in man’s Divine service isדְּעִנְיַן הַבִּטּוּל דְּרֹאשׁ חֹדֶשׁ בַּעֲבוֹדַת הָאָדָם הוּא
not that his identity is totally erased, but rather that his identity does exist but is characterized by bittul.שֶׁהַמְּצִיאוּת שֶׁלּוֹ הִיא בְּבִטּוּל.
{3It is possible to explain that this is the intent of the explanation in the maamar in Torah Or[וְיֵשׁ לוֹמַר דְּזֶהוּ שֶׁמְּבֹאָר בְּתוֹרָה אוֹר
that Rosh Chodesh is called yom hazeh, “this day” (with no accompanying description):דְּזֶה שֶׁרֹאשׁ חֹדֶשׁ נִקְרָא יוֹם הַזֶּה (סְתָם)
“This day” refers to love of G‑d characterized by bittul.הוּא כִּי יוֹם הַזֶּה הוּא אַהֲבָה שֶׁבִּבְחִינַת בִּטּוּל
To explain:
[“Day” is identified with light, as it is written:4 “And G‑d called the light ‘day’ ”;[דְּיוֹם הוּא אוֹר כְּמוֹ שֶׁכָּתוּב וַיִּקְרָא אֱלֹקִים לָאוֹר יוֹם
love is also identified with “light,” as will be explained immediately below.וְאַהֲבָה הִיא אוֹר,
Zeh, “this,” reflects yichuda ila’ah, “the sublime unity,” i.e., a state of utter oneness with G‑d.וְזֶה הוּא יִחוּדָא עִלָּאָה
(Therefore, Moshe Rabbeinu – in contrast to all other prophets – began his prophecies with the word Zeh.)5(שֶׁלָּכֵן מֹשֶׁה רַבֵּנוּ נִתְנַבֵּא בְּזֶה),
All the other prophets began their prophecies with the word Koh, “So” – i.e., like this – “spoke G‑d.” In contrast, Moshe Rabbeinu’s identity was subsumed in G‑dliness to the point where he had no independent identity. He would speak in the first person when speaking in G‑d’s name, as it is written:6 “I will grant the rain for your land at its proper time… I will provide grass in your fields.” Hence, he could say,7 “This is what G‑d has commanded.”
Thus, the expression “this day” points to love that is characterized by bittul, which reflects yichuda ila’ah, the sublime unity].וְיוֹם הַזֶּה הוּא אַהֲבָה שֶׁבִּבְחִינַת בִּטּוּל דְּיִחוּדָא עִלָּאָה],
Generally, in a love relationship the identity of the person who loves is still felt –yesh mi she’oheiv, in chassidic terminology.8 On the level of yichuda ila’ah, everything – even one’s love – is subsumed in oneness with G‑d.
One of the reasons why love is identified with lightכִּי מֵהַטְּעָמִים עַל זֶה שֶׁאַהֲבָה נִקְרֵאת בְּשֵׁם אוֹר,
is that love involves extending oneself outward.9 Just as light radiates forth and gives expression to its source, love motivates a person to express himself to others.הוּא, לְפִי שֶׁאַהֲבָה הִיא הִתְפַּשְּׁטוּת
[Therefore, conversely, fear, which involves contraction, withdrawing into oneself,[וְלָכֵן הַיִּרְאָה שֶׁהִיא כִּוּוּץ
(the opposite of extending oneself,)(הֵפֶךְ הַהִתְפַּשְּׁטוּת)
is identified with darkness]. The light of the person’s soul is in a state of withdrawal.נִקְרֵאת בְּשֵׁם חֹשֶׁךְ],
The bittul of Rosh Chodesh is not expressed through the nullification of one’s being,וְהַבִּטּוּל דְּרֹאשׁ חֹדֶשׁ הוּא לֹא בְּאֹפֶן שֶׁמִּתְבַּטֵּל מִמְּצִיאוּתוֹ
(as is the bittul of fear,)(דֻּגְמַת הַבִּטּוּל דְּיִרְאָה),
but rather that his self-expression (his existence) should be characterized by bittul.}כִּי אִם, שֶׁהַהִתְפַּשְּׁטוּת (הַמְּצִיאוּת) שֶׁלּוֹ הִיא בְּבִטּוּל].
Based on the above, it is possible to explain the connection between the two aspects of Rosh Chodesh Sivan,וְעַל פִּי זֶה יֵשׁ לְבָאֵר הַקֶּשֶׁר דִּשְׁנֵי הָעִנְיָנִים שֶׁבְּרֹאשׁ חֹדֶשׁ סִיוָן
(the bittul of the moon and the perfection of the fundamental emotional attributes):(בִּטּוּל הַלְּבָנָה וְהַשְׁלָמַת עִקְּרֵי הַמִּדּוֹת),
For the birth of the new moon teaches how one’s very existence and identity should be characterized by bittul.כִּי עִנְיַן מוֹלַד הַלְּבָנָה הוּא שֶׁהַמְּצִיאוּת הוּא בְּבִטּוּל.

Summary

There is a conceptual difficulty in the above explanations because the maamar in Torah Or associates the completion of the refinement of the primary emotional attributes (which seemingly highlights man’s attainment of shleimus) with the fact that Rosh Chodesh represents the birth of the new moon (which highlights bittul).
In resolution, the birth of the new moon underscores the renewal of the moon’s existence. The fact that the moon is merely a point at the time of its birth highlights the fact that its light is characterized by bittul.
Similar concepts apply to the Jewish people: The parallel to the bittul of Rosh Chodesh in man’s Divine service is not that one’s identity is completely erased, but rather that his identity exists, but is characterized by bittul.
In that vein, Rosh Chodesh is called “this day.” “This day” refers to love characterized by bittul. Although love generally involves extending oneself outward, in this instance the love itself is characterized by bittul.