This refers to the seventh month of the Hebrew calendar. Alternate translation: "On day 1 of month 7" (See: [[rc://en/ta/man/translate/translate-hebrewmonths]] and [[rc://en/ta/man/translate/translate-ordinal]])
"gather together to worship and honor Yahweh." The phrase "a holy assembly" means the people gather together to worship Yahweh. Worshiping Yahweh is a holy event.
The word "you" refers to the people of Israel who here represent the priests. The priests blew the trumpet to begin a worship service or to gather the community together. Alternate translation: "It will be a day when the priests blow trumpets" (See: [[rc://en/ta/man/translate/figs-synecdoche]])