"It will be a day when the priests blow trumpets". 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. This is also known as "The Feast of Trumpets". Be sure to look back to Exodus 23:16, Exodus 34:22 and Numbers 28:26 to recall the Feasts of Harvest, Ingathering and Weeks.