Moses approached his father in law Jethro and informed him that they will be making their way toward their destiny, the land of Canaan. He urged Jethro to join them, for Jethro would be treated well. Jethro declined the offer, stating that he will return to his home. Moses continued his urging, but now he changed his tactics. Previously he had noted the benefits Jethro would receive by staying with the nation of Israel. When that didn’t work Moses appealed to Jethro’s altruistic side.
“He said, ‘Please do not forsake us, for you know our encampments in the wilderness, and you have been eyes for us.” (Numbers 10:31)
Rashi notes that “you have been eyes for us” could refer to the past or to the future. It is possible that Moses was appealing to all the investment that Jethro had already poured into the nation of Israel. He had been their “eyes,” seeing things that they could not see for themselves because of his unique perspective as an outsider. Alternatively, Moses was addressing the future. As someone with a different perspective Jethro would be in a position to advise Israel as they progressed toward and settled in the promised land. Either way, Moses was calling on the contributions of Jethro in his persuasive argument.
It is not clear whether Jethro acceded to Moses’ request or not. There are differing opinions among the commentators whether Jethro remained or left. Regardless, the method of persuasion is noteworthy. We instinctively feel that people are going to act in a way most beneficial to themselves. This is why Moses initially told Jethro of the benefits he’d receive if he remained with the nation of Israel. However, what motivates people more than benefits is the ability to give. Our feeling of self-worth is often (unfortunately) linked to our ability to contribute. Ultimately, the stronger argument for Jethro to remain was to show how much he had given, or would give, to the nation of Israel.
I don’t know whether this applies on a group level. I doubt very much that Great Britain would have been more inclined to remain in the EU on the basis of an argument that their presence makes the EU so much stronger and more stable. But individuals are very much moved by their ability to give, more so than their potential receipt of good.
This same tool was employed earlier in the Parsha. “Hashem spoke to Moses, saying: Take the Levites from among the Children of Israel and purify them.” (ibid 8:5-6) Moses was in the process of dedicating the Levite tribe to their special service of God. They were singled out for this purpose, which made them different from the other tribes. Indeed this dedication precluded the Levite tribe from inheriting their own estates in the land of Israel. This had major repercussions, and Moses’ job was cut out for him to maintain the goodwill of the Levites in this endeavor.
The Midrash (cited by Rashi) tells us that the phrase “take the Levites” means to persuade them. ‘Take them with words,’ Moses was instructed. ‘Tell them how fortunate they are to be chosen to serve God in such close proximity.’
There were other arguments that Moses could have used to bring the Levites on board. There were numerous advantages that the Levites would gain by this role. They would be given tithes from all produce and they would be exempt from many of the taxes imposed on the rest of the people. But the Midrash states that it was the great privilege of contributing to the service of God that was utilized as the primary lure. That was guaranteed to work better than highlighting the personal gain.