Reference for Arakhin 26:21

כיון דחדא עבידתא עבדי וחד גברא עביד בהו קרי להו חד:

NO MINOR COULD ENTER THE COURT OF THE SANCTUARY TO TAKE PART IN THE SERVICE EXCEPT WHEN THE LEVITES STOOD UP TO SING.<span class="x" onmousemove="('comment',' According to Rashi minors were not admitted at all to any service in the Sanctuary except to join the Levites in the singing. Maimonides, however, refers this passage to the introduction of young priests and Levites to the service, who, even after having reached maturity. could enter the Sanctuary for first time participation in the service, only when the Levites, standing on the platform, were singing.');">⁹</span>

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