Acts 27:9-11 ESV “Since much time had passed, and the voyage was now dangerous because even the Fast was already over, Paul advised them, saying, “Sirs, I perceive that the voyage will be with injury and much loss, not only of the cargo and the ship, but also of our lives.””
The “Fast” is the Day of Atonement. Luke mentions “the Fast” as a casual aside with no explanation. He clearly expects that his readers would understand that the Fast is the Day of Atonement and also when it occurs— the 10th day of the 7th lunar month in the Hebrew calendar and which occurs between the middle of September and the middle of October in the Gregorian calendar. Many Christian readers today may have difficulty understanding this Day of Atonement reference. The level of assumed Jewish knowledge in this text suggests that all believers at that time were more Jewish in their ways than Christians are today.