בַּיּ֣וֹם הַה֗וּא אָ֣ז נָתַ֤ן דָּוִיד֙ בָּרֹ֔אשׁ לְהֹד֖וֹת לַיהוָ֑ה בְּיַד־אָסָ֖ף וְאֶחָֽיו׃ (פ)
Then on that day did David first ordain to give thanks unto the LORD, by the hand of Asaph and his brethren.
Read kabbalistic (mystical) interpretation of I Chronicles 16:7: and classical mystical sources.