And they assembled themselves at Jerusalem in the third month of the fifteenth year of the reign of Asa.

So they came together at Jerusalem in the third month, in the fifteenth year of the rule of Asa.

And when they had arrived in Jerusalem, in the third month, in the fifteenth year of the reign of Asa,

In the third month - i. e. the month Sivan Esther 8:9, corresponding with our June.

The third month - At the feast of pentecost which was held on the third month.

So they gathered themselves together at Jerusalem in the (e) third month, in the fifteenth year of the reign of Asa.
(e) Called Shiuam, containing part of May and part of June.

So they gathered themselves together at Jerusalem,.... By the order of Asa, 2-Chronicles 15:9,
in the third month; of the ecclesiastical year, the month Sivan, in which month was the day of Pentecost; and that very probably was the time of their gathering:
in the fifteenth year of the reign of Asa; and which seems to be the year in which he fought the Ethiopians.

the third month--when was held the feast of pentecost. On this occasion, it was celebrated at Jerusalem by an extraordinary sacrifice of seven hundred oxen and seven thousand sheep, the spoil of the Ethiopians being offered. The assembled worshippers entered with great and holy enthusiasm into a national covenant "to seek the Lord their God . . . with all their heart and with all their soul;" and, at the same time, to execute with rigor the laws which made idolatry punishable with death (2-Chronicles 15:13; Deuteronomy 17:2-5; Hebrews 10:28). The people testified unbounded satisfaction with this important religious movement, and its moral influence was seen in the promotion of piety, order, and tranquillity throughout the land.

At this festival, which was held on the third month of the fifteenth year of Asa's reign, they offered of the booty, i.e., of the cattle captured in the war against the Cushites (2-Chronicles 14:14), 700 oxen and 7000 sheep. הביאוּ מן־השּׁלל defines the ויּזבּחוּ more closely: they sacrificed, viz., from the booty they offered. From this it seems to follow that the sacrificial festival was held soon after the return from the war against the Cushites. The attack of the Cushite Zerah upon Judah can only have occurred in the eleventh year of Asa, according to 2-Chronicles 14:1; but it is not stated how long the war lasted, nor when Asa returned to Jerusalem (2-Chronicles 14:14) after conquering the enemy and plundering the towns of the south land. But Asa may quite well have remained longer in the south after the Cushites had been driven back, in order again firmly to establish his rule there; and on his return to Jerusalem, in consequence of the exhortation of the prophet Azariah, may have straightway determined to hold a sacrificial festival at which the whole people should renew the covenant with the Lord, and have set apart and reserved a portion of the captured cattle for this purpose.