Since internal union is the surest safeguard against persecution from without, Rashi earnestly exhorted his brethren to shun intestine strife. "Apply yourselves to the cultivation of peace," he once wrote. "See how your neighbors are troubled by the greatest evils and how the Christians delight in them. Concord will be your buckler against envy and prevent it from dominating you." In a community, doubtless that of Chalons- sur-Saone, in Burgundy,[127] there were two families that quarrelled [quarreled sic] continually. The community had intervened to stop the strife, but one of the two families declared in advance that it would not submit to its decision. A member of the other family, irritated, reproached one of his enemies with having been baptized. Now Rabbenu Gershom, under penalty of excommunication, had forbidden people to recall his apostasy to a converted Jew. Rashi was asked to remove this prohibition; but he declined, not wishing to intervene in the internal administration of a strange community. "What am I that I should consider myself an authority in other places?... I am a man of little importance, and my hands are feeble, like those of an orphan. If I were in the midst of you, I would join with you in annulling the interdiction." From this it is evident that the strongest weapon of the rabbinical authorities against the intractable was, as in the Church, excommunication; but that sometimes individuals asserted, and even swore in advance, that they would not yield to the decree against them. Rashi considered that this oath, being contrary to law, was null and void.