שֶׁ֣֭עֹֽמְדִים בְּבֵ֣ית יְהוָ֑ה בְּ֝חַצְר֗וֹת בֵּ֣ית אֱלֹהֵֽינוּ׃
Ye that stand in the house of the LORD, In the courts of the house of our God.
Ibn Ezra on Psalms
"Who stand" - those are the priests who perform the sacrifices and those who play the trumpets