(א) אַרְבָעָה דְּבָרִים נֶאֶמְרוּ בְּשַׁבָּת. שְׁנַיִם מִן הַתּוֹרָה. וּשְׁנַיִם מִדִּבְרֵי סוֹפְרִים וְהֵן מְפֹרָשִׁין עַל יְדֵי הַנְּבִיאִים. שֶׁבַּתּוֹרָה (שמות כ-ז) "זָכוֹר" וְ (דברים ה-יא) "שָׁמוֹר". וְשֶׁנִּתְפָּרְשׁוּ עַל יְדֵי הַנְּבִיאִים כָּבוֹד וָעֹנֶג שֶׁנֶּאֱמַר (ישעיה נח-יג) "וְקָרָאתָ לַשַּׁבָּת עֹנֶג וְלִקְדוֹשׁ ה' מְכֻבָּד":
(1) Four concepts were said regarding Sabbath, two from the Torah, and two from the words of the Sages and explicated through the Prophets. From the Torah: "Remember" (Exodus 20:8) and "Observe" (Deuteronomy 5:12). And explicated through the Prophets: Honor and delight, as it is said, "And call the sabbath a delight, And the holy of the LORD honourable" (Isaiah 58:13).
(טז) כְּשֵׁם שֶׁמִּצְוָה לְכַבֵּד שַׁבָּת וּלְעַנְּגָהּ כָּךְ כָּל יָמִים טוֹבִים שֶׁנֶּאֱמַר (ישעיה נח-יג) "לִקְדוֹשׁ ה' מְכֻבָּד" וְכָל יָמִים טוֹבִים נֶאֱמַר בָּהֶן (ויקרא כג-ז) "מִקְרָא קֹדֶשׁ". וּכְבָר בֵּאַרְנוּ הַכִּבּוּד וְהָעִנּוּג בְּהִלְכוֹת שַׁבָּת. וְכֵן רָאוּי לְאָדָם שֶׁלֹּא יִסְעֹד בְּעַרְבֵי יָמִים טוֹבִים מִן הַמִּנְחָה וּלְמַעְלָה כְּעֶרֶב שַׁבָּת שֶׁדָּבָר זֶה בִּכְלַל הַכָּבוֹד. וְכָל הַמְבַזֶּה אֶת הַמּוֹעֲדוֹת כְּאִלּוּ נִטְפָּל לַעֲבוֹדַת כּוֹכָבִים:
(16) In the same way that there is an obligation to honor the Sabbath and to delight in it those obligations apply to the festivals. As it is stated (Isaiah 58:13) "to the Holy God who is honored" and all of the holidays are referred to as (Leviticus 23:7) "a time of holiness". We have already addressed the ideas of honor and delight in the laws of the Sabbath. It is therefore fitting for a person to refrain from feasting on the eve of festivals from the time of minha just as we do on Sabbath eve as this is part of obligation of honoring. And, anyone who disgraces the festivals, it is as if he as served foreign worship.
(14) And you shall rejoice in your feast, you, and your son, and your daughter, and your man-servant, and your maid-servant, and the Levite, and the stranger, and the fatherless, and the widow, that are within your gates.
(י) וּבְי֨וֹם שִׂמְחַתְכֶ֥ם וּֽבְמוֹעֲדֵיכֶם֮ וּבְרָאשֵׁ֣י חָדְשֵׁיכֶם֒ וּתְקַעְתֶּ֣ם בַּחֲצֹֽצְרֹ֗ת...
(10) Also in the day of your gladness, and in your designated holidays, and in your new moons, you shall blow with the trumpets over your burnt-offerings...
אבן עזרא במדבר י:י
Ibn Ezra Bamidbar 10:10
'and on the day of your joy and on your appointed holidays' on those days which you return [victorious] from the land of your enemy who descends upon you. And you shall fix them as days of joy such as we have done with Purim or the Seven Days of Hizkiah...
(א) וביום שמחתכם (ובמועדיכם) אלו שבתות. ר' נתן אומר אלו תמידים. ובמועדיכם אלו שלש רגלים. ובראשי חדשיכם כמשמעו...
(1) (Bamidbar 10:10) "And on the day of your rejoicing and on your appointed times you shall sound the trumpets": "And on the day": Sabbaths. R. Nathan says: These are temidim (the daily burnt-offerings). "your rejoicings": These are the three festivals. "and in your appointed times": These are Rosh Hashanah and Yom Kippur. "and on your new moons": as stated. "over your burnt-offerings and over the sacrifices of your peace-offerings"...
בן זומא אומר: ..איזהו עשיר? השמח בחלקו, שנאמר: (תהלים קכח ב): "יגיע כפיך כי תאכל אשריך וטוב לך".אשריך, בעולם הזה .וטוב לך, לעולם הבא.
...Who is the rich one? He who is happy with his lot, as it says, "When you eat [from] the work of your hands, you will be happy, and it will be well with you" (Psalms 128:2). "You will be happy" in this world, and "it will be well with you" in the world to come.
...מאמר מר שמניחין חיי עולם ועוסקין בחיי שעה והא שמחת יום טוב מצוה היא...
...it was said by Mar: "we should set asside life eternal [the learning of Torah] to engage in issues of life temporary [to engage in feasting]!? Is rejoicing on the festivals not a mitzvhah!? (...)
The Collected Writings of Rav S.R. Hirsch 2:3:4 page 85-86
The three pilgrimage holidays occur at times which, in a nature way arouse joy. The spring, the harvest and the gathering all in their nature cause joy. It is incumbent upon a person to direct this joy to become the joy of mitzvah, to become the spiritual joy in the commandments of hashem.
Zohar
The mystery of Sabbath: Sabbath is unification through oneness, which causes the mystery of oneness to dwell upon it. Prayer, which the Sabbath raises up, unifies and perfects the holy and precious throne through the mystery of oneness so that the divine and holy King may sit upon it. When the Sabbath begins, she is made one and separates from the other side [i.e., evil] and all the forces of severity pass away. She remains unified with the holy light and is adorned with many crowns by the holy King. All the powers of ire and forces of severity are uprooted and there is no evil dominion upon the worlds. Her face is radiant with divine light and she is adorned below with the holy people.
בָּרוּךְ אַתָּה ה'. מְקַדֵּשׁ הַשַּׁבָּת:
Blessed are you Hashem who sanctifies Shabbat.