The custom of playing with bows and arrows on Lag BaOmer, the day that marks the passing of Rabbi Shimon bar Yochai, symbolizes our sages proclamation that not a single rainbow appeared in the sky during the lifetime of this great sage.
The rainbow first appeared after the flood, and represents G‑d's promise to never again destroy the world by flood. The rainbow appears when the world is deserving of punishment. The merit of Rabbi Shimon bar Yochai protected his entire generation and no rainbow appeared during his lifetime.
The Hebrew word for rainbow, keshet, also translates as bow.
Please see The Kabbalah of the Bow and Arrow from our Lag BaOmer section.
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