The LORD said to Moses: Say to the Israelites: On the first day of the seventh month, you will have a special rest, a holy occasion marked by a trumpet signal. You must not do any job-related work, and you must offer a food gift to the LORD. – Leviticus 23:23-25 (CEB)
The first day of the seventh month[a] will be a holy occasion for you. You will not do any job-related work. It will be for you a day of the trumpet’s sound. – Numbers 29:1 (CEB)
This year, Rosh Hashanah runs until sunset on September 30. It’s a time of celebration (as you might have guessed from the trumpets!) but also of repentance and reflection.
Most Christians don’t observe Rosh Hashanah (or other Jewish holidays) today, but I’ve seen shofars used in evangelical worship services on rare occasions, either to mark the date or to evoke the celebratory spirit of ancient Israelite holidays. If you want to learn more, see the Wikipedia entry on Rosh Hashanah, or read six ways to usher in the Jewish New Year at the Velveteen Rabbi blog.
Image shows a shofar being sounded. Photo by Flickr user slgckgc.