Bnei Yissaschar, Iyar 3:4/בני יששכר·אייר ג׳:ד׳

1One particular custom practiced on the day of Lag B'Omer is unique: Children go to parks and fields to play with bows and arrows. What is the reason for this peculiar custom? One well-known explanation[5] has to do with the fact that during Rabbi Shimon's lifetime, no rainbow ever appeared in the sky[6]. This is profoundly significant, because Genesis relates[7] that the rainbow represented G-d's covenant never to destroy the world again even if the human race would degenerate to its status prior to the Flood. But as long as Rabbi Shimon was alive, his merit and piety alone were enough to ensure that G-d would not regret His creation, with no need for the rainbow. On the day of Rabbi Shimon's passing, however, the world was in need of the rainbow. Thus, each year on that day we recall this man's greatness by playing with the bow[8].