Genesis 2:1-3

וַיְכֻלּ֛וּ הַשָּׁמַ֥יִם וְהָאָ֖רֶץ וְכָל־צְבָאָֽם׃
1 And the heavens and the earth were completed, and all their army.

According to several Church Fathers (XXC), this refers to the heavenly army of angels.

וַיְכַ֤ל אֱלֹהִים֙ בַּיֹּ֣ום הַשְּׁבִיעִ֔י מְלַאכְתֹּ֖ו אֲשֶׁ֣ר עָשָׂ֑ה וַיִּשְׁבֹּת֙ בַּיֹּ֣ום הַשְּׁבִיעִ֔י מִכָּל־מְלַאכְתֹּ֖ו אֲשֶׁ֥ר עָשָֽׂה׃
2 And Elohim finished on the seventh day the work he had done, and he ceased on the seventh day all the work he had done.

וַיְבָ֤רֶךְ אֱלֹהִים֙ אֶת־יֹ֣ום הַשְּׁבִיעִ֔י וַיְקַדֵּ֖שׁ אֹתֹ֑ו כִּ֣י בֹ֤ו שָׁבַת֙ מִכָּל־מְלַאכְתֹּ֔ו אֲשֶׁר־בָּרָ֥א אֱלֹהִ֖ים לַעֲשֹֽׂות׃
3 And Elohim blessed the seventh day and sanctified it, because on it He Elohim ceased every work that he created to be done.

Moses Nahmanides, acronym Ramban (Gerona, 1194 – Acre, 1270) on Genesis 2:1

וְכָל צְבָאָם. « צבא הארץ » הם הנזכרים חיה ורמש ודגים וכל הצומח גם האדם ו »צבא השמים » שני המאורות והכוכבים הנזכרים כענין וּפֶן תִּשָּׂא עֵינֶיךָ הַשָּׁמַיְמָה וְרָאִיתָ אֶת הַשֶּׁמֶשׁ וְאֶת הַיָּרֵחַ וְאֶת הַכּוֹכָבִים כֹּל צְבָא הַשָּׁמַיִם (דברים ד יט) גם יכלול השכלים הנבדלים כענין רָאִיתִי אֶת ה’ יֹשֵׁב עַל כִּסְאוֹ וְכָל צְבָא הַשָּׁמַיִם עֹמֵד עָלָיו וגו’ (מלכים א כב יט) וכן יִפְקֹד ה’ עַל צְבָא הַמָּרוֹם בַּמָּרוֹם (ישעיהו כד כא) והנה בכאן רמז על יצירת המלאכים במעשה בראשית וכן נפשות האדם צבא השמים הנה

And all their army. “The army of the earth” refers to those who have been mentioned, animals, reptiles, fish, everything that grows, and also man. And “the army of heaven” refers to the two luminaries, the stars that have been mentioned, as in the verse in Deuteronomy 4:19: «And when you look up to the heavens and behold the sun or the moon or any star among the heavenly hosts, do not be led astray into adoring them and serving them.» This also includes the separate intellects, as in the verse in 1 Kings 22:19: “I saw the Lord sitting on his throne, and all the army of heaven standing before him,” and also in the verse from Isaiah 24:21: “Thus the Lord rewards the army of the heights in the heights (and the kings of the earth on earth).” Thus, here we have an allusion (a symbol) to the formation of angels in the work of Genesis. And also, the souls of men are also the army of heaven.

Moses Nahmanides, acronym Ramban (Gerona, 1194 – Acre, 1270) on Genesis 2:3

הַיוֹם הַשְׁביעי שַבָּת, רמז לָעוֹלֶם הַבִָֹֹּא שֶׁכֻּלּוֹ שַבָּת וּמְנּחָה לחיֵּי הָעוֹלָמִים

The seventh day, shabbat-cessation, is a symbol of the world to come, which is entirely shabbat-cessation and rest for eternal life.

Keli Yakar (Salomon Ephraim de Luntschitz (1550 Łęczyca, Poland – 1619 Prague) on Genesis 2:3

וּמָה שֶלֹּא נֶאֱמַר בְּשַׁבַּת וַיְהִי עֶרֶב וַיְהִי בֹקָר. לְפִי שֶבְּכָל הַיַמִים הַלַּיְלָה זְמַן הַמְּנוּחָה וְהַבֹּקֶר זְמַן הַמְּלָאכָה כְּמוֹ שֶׁנֶּאֱמַר (תְּהִלִּים קד כב) תִּזְרַח הַשֶּׁמֶשׁ יֵאָסֵפוּן וְגוֹ׳ יֵצֵא אָדָם לְפַעֳלוֹ. אֲבָל יוֹם הַשַּבָּת אוֹ כֻלּוֹ מְנוּחָה אוֹ כֻלּוֹ מְלָאכָה אִם כֵּן אֵין בּוּ הֶבְדֵּל בֵין עֶרֶב לְבֹקֶר כִּי מִצַּד סְתָם מְלָאכָה כֻּלּוֹ מְנוּחָה. וּמִצַּד עֲמַל הַתּוֹרָה כֻּלּוֹ לִמְלָאכָה כִּי יוֹם הַשַׁבָּת נִתַּן לַעֲסֹק בּוֹ בַּתּוֹרָה, שֶׁנֶּאֱמַר בַּהּ (יְהוֹשֻׁעַ א ח) וְהָגִיתָ בּוֹ יוֹמָם וָלַיְלָה. וְכִדְאִיתָא בַּמִּדְרָש. (תדא״ר א.) וְאוּלַי שֶׁעַל זֶה נֶאֱמַר, כִּי בוֹ שָׁבַת מִכָּל מְלַאכְתּוֹ אֲשֶׁר בָּרָא. הַיְינוּ סְתָם מְלָאכָה, לַעֲשׂוֹת. בַּחֲרֹשֶׁת עֶץ חַיִּים הַתּוֹרְנִי, וּבַחֲרֹשֶַת אֶבֶן הַלוּחוֹת, וְקָל לְהָבִין.

Why (during the work of creation) on the day of Shabbat is it not said: “It was evening, and it was morning”? Because every day, night is considered a time of rest and morning a time of work, as it is said in Psalm 104:22-23: “The sun shines, they gather together… man goes forth to his work.” But on the Sabbath day, it is either entirely rest or entirely work. If this is so, there is no division between evening and morning, since in the sense of simple work, it is entirely rest. In the sense of working on the Torah, it is entirely for work, since the Sabbath day was given to devote oneself to the Torah, as it is said in the book of Joshua 1:8: “You shall meditate on it day and night.” And likewise it is reported in the Midrash (Tana debe Eliyahu rabba 1). And perhaps it is in the same sense that it is said that in it (in the Sabbath) He ceased all His work of creation. That is, work in the simple sense, to labor in meditation (or: in the grove) of the tree of life of the Torah and in the engraving of the stone tablets (of the Law), is easy to understand.

For an analysis of all the seven days, see the article Genesis 1,1 – 2,3