This is a reference to the major Jewish holidays that fall in quick succession in the Hebrew month of Tishrei, in the fall: Rosh Hashanah (the "feast of trumpets," alluding to the shofar or ram's horn, which is blown on this holiday), Sukkoth (the "feast of the tabernacles," also known as "the feast of the booths," on account of the temporary dwellings Jews build for the holiday) and the fasts of Gedaliah (a minor fast) and Yom Kippur (known as the Day of Atonement, a major holiday and fast day).
For those of you who are unfamiliar with these holidays, some brief explanations to help explain why these festivals may have been attractive to Christians in Antioch:
Rosh Hashanah Rosh Hashanah is the Jewish New Year festival. It celebrates the creation of the world, and is a time for reflection and self-assessment, with solemn prayers conducted in the synagogue. It is held on the first and second days of the month of Tishrei (usually in September - the Jewish calendar is lunar). The biblical terms for the holiday are Yom ha-zikkaron (the day of remembrance) or Yom Teruah (the day of the blowing of the shofar). For its biblical origins, see Leviticus 23:24-25.
Fast of Gedaliah This is not a major holiday, but a fast day commemorating a historical event. In the ancient period, such fasts were held outdoors in public. As on other fast days, Jews refrained from wearing leather shoes on this day - a prescribed form of mourning in Jewish law. The historical event being commemorated was this: After the capture of Jerusalem and destruction of the Temple by the Babylonians in 586 BCE, Gedaliah ben Achikam was appointed by the Babylonians as governor of the impoverished remnant of Jews in Judah. (Many had been forced into exile.) The king of the Ammonites, attempting to weaken Babylonian influence in the region, sent a Jew by the name of Yishmael ben Netaniah to assassinate Gedaliah. The assassination turned into a general massacre. To mark this tragic end to Jewish autonomy in the Land of Israel the "Fast of the Seventh [Month]" was proclaimed by the prophet Zechariah (Zechariah 7:5). According to tradition, the fast falls on the third of Tishrei.
Yom Kippur Yom Kippur is both a major holiday and a fast day, and falls on the tenth of Tishrei. Yom Kippur means "Day of Atonement"; it is a day of fasting and prayer, a day to perform repentance and to seek atonement from God. It combines fasting and celebration, personal self-affliction and collective joy, in a complex way. For its biblical origins, see Leviticus 23:26-32.
Sukkot The festival of Sukkot begins on 15 Tishrei and lasts for a week. During this period, Jews live in temporary huts or booths to commemorate the period when the Israelites lived in the wilderness. There are other festive activities associated with the holiday, including the mandated "rejoicing before the Lord" with the lulav (palm, willow, and myrtle branches) and etrog (citron). For the holiday's biblical origins, see Leviticus 23:33-36.