And the people of Israel who were present at that time kept the passover and the feast of unleavened bread seven days: The passover and the feast of unleavened bread were originally, technically, two different festivals, with the passover referring to the evening of the first day and the feast of unleavened bread to the next seven days, but it became a single integrated observance. See Exo 12.1-20 for the origins of these two festivals. The feast of unleavened bread was held in the first Hebrew month, from the fifteenth day until the twenty-first day, which is roughly equivalent to early April in the modern Western calendar. This festival took place immediately after Passover, also in commemoration of the deliverance of the Israelites from their slavery in Egypt. Its name came from the practice of not using leaven (yeast) in making bread during that week. Good News Bible has a helpful model for this verse.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Esdras. (UBS Helps for Translators). Miami: UBS, 2019. For this and other handbooks for translators see here.