Regarding what is the way to investigate on the truth of the unity, and what introductions we need to know before we investigate on this unity, I will say as follows.
Any matter which one would like to understand when one is in doubt of its very existence, must first ask "does it exist or not?" After one has established its existence, one must then enquire as to what it is, how it is, and why it is. But regarding the Creator, a man may only ask whether He exists. And when His existence is demonstrated through rational investigation, we may further enquire whether He is one or more than one. And when it is clear that He is one, we may enquire on the matter of unity, and on how many ways this term is used, and in this way we will establish for ourselves the complete recognition of the unity of G-d, as the verse says: "Hear O Israel, the L-ord is our G-d, the L-ord is One" (Deut. 6:4).
Therefore, we must first enquire whether or not this world has a Creator. When it becomes clear that the world has a Creator who created it as something new, we can then further enquire whether He is one or more than one. Then, when it will be established that He is one, we can investigate into the matter of true (absolute) Unity and temporary (relative) unity, and then consider what we can say of the Creator regarding His true matter, and through this we will have completed the matter of acknowledgement of the unity of G-d in our hearts and minds, with G-d's help.
אַךְ אֵיךְ דֶּרֶךְ הַמֶּחְקָר עַל אֲמִתַּת הַיִּחוּד וּמָה שֶׁאָנוּ צְרִיכִין לְדַעְתּוֹ קֹדֶם שֶׁנַּחְקֹר עַל הַיִּחוּד אוֹמַר,
Regarding what is the way to investigate on the truth of the unity, and what introductions we need to know before we investigate on this unity, I will say as follows.
כִּי כָל דָּבָר שֶׁמְּבַקְשִׁים לָדַעַת אוֹתוֹ כְּשֶׁמִּסְתַּפְּקִים בִּמְצִיאוּתוֹ צָרִיךְ לִשְׁאוֹל עָלָיו תְּחִלָּה אִם הוּא נִמְצָא אִם לֹא וּכְשֶׁתִּתְבָּרֵר אֲמִתַּת מְצִיאוּתוֹ צָרִיךְ לַחְקֹר עָלָיו מַהוּ וְאֵיךְ הוּא וְלָמָּה הוּא. אַךְ הַבּוֹרֵא יִתְעַלֶּה אֵין אָדָם רַשַּׁאי לִשְׁאוֹל עָלָיו אֶלָּא בְּאִם הוּא בִּלְבַד. וּכְשֶׁתִּתְבָּרֵר מְצִיאוּתוֹ בְּדֶרֶךְ הָעִיּוּן נַחְקֹר עָלָיו אִם הוּא אֶחָד אוֹ יוֹתֵר מֵאֶחָד. וְכַאֲשֶׁר יִתְבָּרֵר לָנוּ שֶׁהוּא אֶחָד נַחְקֹר עַל עִנְיַן הָאֶחָד וְעַל כַּמָּה פָּנִים יֵאָמֵר אֶחָד וּבָזֶה יִתְקַיֵּם לָנוּ הַיִּחוּד הַשָּׁלֵם כְּמוֹ שֶׁאָמַר הַכָּתוּב (דברים ו) שְׁמַע יִשְׂרָאֵל ה׳ אֱלֹהֵינוּ ה׳ אֶחָד.
Any matter which one would like to understand when one is in doubt of its very existence, must first ask "does it exist or not?" After one has established its existence, one must then enquire as to what it is, how it is, and why it is. But regarding the Creator, a man may only ask whether He exists. And when His existence is demonstrated through rational investigation, we may further enquire whether He is one or more than one. And when it is clear that He is one, we may enquire on the matter of unity, and on how many ways this term is used, and in this way we will establish for ourselves the complete recognition of the unity of G-d, as the verse says: "Hear O Israel, the L-ord is our G-d, the L-ord is One" (Deut. 6:4).
עַל כֵּן אֲנַחְנוּ חַיָּבִים לַחְקֹר תְּחִלָּה הַיֵּשׁ לעוה״ז בּוֹרֵא אִם לֹא. וְכַאֲשֶׁר יִתְבָּרֵר לָנוּ שֶׁיֵּשׁ לָעוֹלָם בּוֹרֵא בְּרָאוֹ וְחִדְּשׁוֹ נַחְקֹר עָלָיו אִם הוּא אֶחָד אוֹ יוֹתֵר מֵאֶחָד וּכְשֶׁיִּתְבָּרֵר כִּי הוּא אֶחָד נַחְקֹר עַל עִנְיַן הָאֶחָד הָעוֹבֵר וְהָאֶחָד הָאֱמֶת. וּמָה שֶׁצָּרִיךְ לְסַפֵּר בּוֹ עַל הַבּוֹרֵא מֵעִנְיָנוֹ וּבוֹ יִשְׁלַם עִנְיַן הַיִּחוּד בְּלִבֵּנוּ וְיִגָּמֵר בְּמַחְשַׁבְתֵּנוּ בעז״ה:
Therefore, we must first enquire whether or not this world has a Creator. When it becomes clear that the world has a Creator who created it as something new, we can then further enquire whether He is one or more than one. Then, when it will be established that He is one, we can investigate into the matter of true (absolute) Unity and temporary (relative) unity, and then consider what we can say of the Creator regarding His true matter, and through this we will have completed the matter of acknowledgement of the unity of G-d in our hearts and minds, with G-d's help.