Then they said, Behold, there is a feast of the LORD in Shiloh yearly in a place which is on the north side of Bethel, on the east side of the highway that goeth up from Bethel to Shechem, and on the south of Lebonah. There is a feast of the Lord - What this feast was is not known: it might be either the passover, pentecost, or the feast of tabernacles, or indeed some other peculiar to this place. All the above feasts were celebrated at that time of the year when the vines were in full leaf; therefore the Benjamites might easily conceal themselves in the vineyards; and the circumstances will answer to any of those feasts.
On the east side of the highway, etc. - I can see no reason for this minute description, unless it intimates that this feast was to be held this year in rather a different place to that which was usual: and, as the Benjamites had been shut up in their strong hold in Rimmon, they might not have heard of this alteration; and it was necessary, in such a case, to give them the most circumstantial information, that they might succeed in their enterprise without being discovered.