Numbers 31:1

But a deeper vengeance is taken on fiercer foes and on those that are false as well as on those who have done greater wrongs, as was the case with the Midianites. For they had made many of the Jewish people to sin through their women. For this reason the anger of the Lord was poured out upon the people of our fathers. Thus it came about that Moses when victorious allowed none of them to live.

In the passages above, the sons of Israel committed fornication with the women of the Midianites, and this was a stumbling-block to the sons of Israel, in which they offended the Lord and provoked to anger the Holy One of Israel. Now therefore, after Israel had suffered what it suffered, "the Lord spoke," it says, "to Moses, saying: Avenge the vengeance of the sons of Israel upon the Midianites, and afterward you shall be added to your people." Therefore, as for the stumbling-blocks that had befallen the Israelites, since they had befallen them through the treachery of the Midianites — for they themselves had suborned the women who were to deceive them, so that they might sin before the Lord — those men indeed suffered punishment for their sin, yet more moderately and more sparingly, whereas these, who were the cause of their sinning, are subjected to a far more severe vengeance. Whence we are taught that it is far graver to furnish others the occasion of sin than for each one himself to sin, just as the Lord also indicates, when He says that: "It were better for a man not to have been born, or that an ass's millstone be tied about his neck and that he be cast into the depth of the sea, than that he should scandalize one of these little ones." And at the same time it must be noted that the name of "scandal" is improperly assumed by some — that a scandal is said to be there, where for one walking on the straight road some deception toward sin is contrived and the cause of sinning is put beneath him, just as also the Midianites, for the Israelites walking in the law of the Lord and keeping chastity, suborned the women who were to deceive them into sinning. Therefore to furnish the cause of sin, this is to scandalize. And yet punishment is given, but far graver upon those who scandalized, who furnished the cause of sin, than upon those who sinned. At the same time observe also that which He added to these things: "but at the last," He says, "you also shall be added to your people." If ever we have discourse with the Samaritans, since indeed they deny the resurrection of the dead and do not accept the faith of the age to come, let us press them hard from these words, in which the Lord says to Moses that he is to be added to his people. For no one is added to those who do not exist. Whence it is established that there is some people to which Moses is said to be…