"Rejoice in Hashem, you righteous"
The scholars decreed that praises on Shabbat should start with the psalms of David, which rise to illuminate and bless the heavens and the river that comes out of Eden. All is performed as it should be performed, though, and on this day even the sun illuminates properly.
David signifies our physical existence. He is Malchut. Thus, David's psalms elevate our lower world (Malchut) into the heavens (Zeir Anpin) when they are recited at the commencement of each new Shabbat. For us, our own souls - and all existence - are now elevated by the sacred texts that speak these hidden truths.
208. And the friends decreed that the praises start with the praises of David, with this secret OF THE PRAISE "THE HEAVENS DECLARE... " The heaven, WHICH IS ZEIR ANPIN, takes first and illuminates all the rest. Afterwards the river that comes out of Eden, WHICH IS YESOD, TAKES and this is the secret of, "Rejoice in Hashem, you righteous" (Tehilim 33:1), FOR THIS PRAISE IS THE ASPECT OF YESOD. This river gathers and takes everything from the secret of the heavens, WHICH IS ZEIR ANPIN, in the supernal secret, WHICH IS CHASSADIM, and the source of life, WHICH IS THE ILLUMINATION OF CHOCHMAH, and all as is proper on this day. The sun, WHICH IS ZEIR ANPIN, perfects YESOD to illuminate properly on this day.
208. וְאַתְקִינוּ חַבְרַיָּיא שֵׁירוּתָא דְּתוּשְׁבַּחְתֵּי, מֵאִינּוּן תּוּשְׁבַּחְתָן דְּדָוִד, מֵרָזָא דָּא הַשָּׁמַיִם, דְּאִיהוּ נָטִיל בְּרֵישָׁא, וְנָהִיר לְכָל שְׁאָר. וּלְבָתַר הַהוּא נָהָר דְּנָפִיק מֵעֵדֶן, וְדָא אִיהוּ רָזָא, רַנְּנוּ צַדִּיקִים בַּיְיָ' בְּגִין דְּהַאי נָהָר כָּנִישׁ וְנָטִיל כֹּלָּא מֵרָזָא דְּשָׁמַיִם, בְּרָזָא עִלָּאָה, וּמְקוֹרָא דְּחַיֵּי, כֹּלָּא כַּדְקָא יֵאוֹת בְּיוֹמָא דָּא. וְשִׁמְשָׁא אַתְקִין לְאַנְהֲרָא כַּדְקָא יֵאוֹת, בְּיוֹמָא דָּא.