Psalm 100 was recited in the Temple only on those days when thank-offerings were offered on the Altar.It is therefore omitted on Shabbos, on Yom Tov, on the day before Yom Kippur, on the day before Pesach, and also on the intermediate days of Pesach, when only obligatory-offerings were offered.
Our Sages declare (Midrash Rabbah Tzav, 9) "In the future, even though all things on earth will be in such an ideal state that there will be no more cause for prayers and offerings, prayers of gratitude, and offerings of thanksgiving will nevertheless not cease."
Ordinarily, when a person is saved from a fatal illness, is released from captivity, or returns from a risky journey, he pronounces the special blessing Hagomeil (see page 177). Our Sages, instituted psalm 100 in our daily prayers as an expression of thanks for the many unrecognized miracles God performs in our behalf every day.
The following Psalm is omitted on Shabbat, Festivals, the day before Pesach, Chol HaMoed, Pesach and the day before Yom Kippur.
מִזְמוֹר לְתוֹדָה A psalm of thanksgiving:
הָרִֽיעוּ לַיהוָֹה כָּל־הָאָֽרֶץ: Shout for joy to Adonoy, everyone on earth.
עִבְדוּ אֶת יְהֹוָה בְּשִׂמְחָה Serve Adony with joy,1To serve God means to devote every moment of one's life to the execution of God's will. We are called upon to dedicate ourselves to this life of Divine service with rejoicing, for only such a life can give us the true joy that comes from constant spiritual and moral growth.—S.R. Hirsch
בֹּֽאוּ לְפָנָיו בִּרְנָנָה: come before Him with exultation.
דְּעוּ כִּי־יְהֹוָה הוּא אֱלֹהִים Know that Adonoy is God,
הוּא עָשָֽׂנוּ וְלוֹ (וְלֹא) אֲנַֽחְנוּ He has made us, and we are His,2As is pointed out by the written form לא, which indicates “we are nothing,” we are not even the most insignificant part of our existence to ourselves. In fact, the more we realize that we are לא, insignificant, the more לו אנחנו, we are His.—Sfas Emes
עַמּוֹ וְצֹאן מַרְעִיתוֹ: His people and the sheep of His pasturing.
בֹּֽאוּ שְׁעָרָיו בְּתוֹדָה Enter His gates3The gates of the Temple Mount. with thanksgiving,
חֲצֵרֹתָיו בִּתְהִלָּה His courtyards4The courts of the holy Temple. with praise.
הֽוֹדוּ לוֹ בָּרְ֒כוּ שְׁמוֹ: Give thanks to Him, bless His Name
כִּי־טוֹב יְהֹוָה for Adonoy is good,
לְעוֹלָם חַסְדּוֹ His loving kindness is eternal,
וְעַד־דֹּר וָדֹר and to every generation
אֱמוּנָתוֹ: His faithfulness [extends.]