In the third month they began to pile up the heaps, and finished them in the seventh month: The third month in the Jewish calendar corresponds to mid-May to mid June in the Gregorian calendar (see the comments on 2 Chr 15.10; see also Ellington’s article on the Jewish calendar in The Bible Translator). It was the time of grain harvest. The seventh month is equivalent to mid-September to mid-October (see the comments on 2 Chr 5.7). It was the time of grape and other fruit harvest. So the whole process of bringing the gifts, which took place during the harvest season, took a total of four months, as indicated by the rendering of Good News Translation. Pentecost was celebrated in the third month; and the Feast of Tabernacles, in the seventh month.

For heaps see the comments on the previous verse.

Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on 1-2 Chronicles, Volume 1. (UBS Helps for Translators). Miami: UBS, 2014. For this and other handbooks for translators see here .