Or HaChaim on Exodus 18:18/אור החיים על שמות י״ח:י״ח

1 נבול תבול, "you will surely become weary, etc." Yitro repeated the word נבול because it has two meanings. We apply this term to describe anything which has lost some of its original strength, and as a result has become weary, fatigued, relative to its original state. Nonetheless the subject under discussion is still able to perform its basic task though with greater exertion. The second meaning of נבול is a feeling of weariness which is felt so keenly that the subject is unable to carry out his regular routine at all. Yitro warned Moses that though, intially, he would feel only slightly weary, eventually he would become so weary, נבול תבול, that he would be unable to function at all. Yitro underlined this by saying: "you will not be able to carry on by yourself." Alternatively, the reason he repeated the word was simply because he wanted to illustrate how both Moses and the litigants would become weary.

2גם אתה גם העם הזה, "both you and this people, etc." Yitro used the word גם twice to indicate that not only Moses whose powers were very great and close to inexhaustible would tire (seeing he had to preside over litigation daily for many hours), but also the people who would have to stand in line would find this too tiresome.

3The Mechilta understands the word גם as referring to Aaron, whereas the word העם would refer to the seventy elders. We need to understand the reason for this interpretation. If they considered only the word גם they would have had to explain these two words in the same way as we have done. However, the sages realised that if Moses would follow Yitro's advice he would have had to appoint close to 80,000 judges. He therefore indicated that even seventy elders were far too few. The sages therefore understood the word גם to refer to the additional judges Moses would have to appoint. They interpreted the second גם to refer to judges in addition to Moses. In each instance the word גם added a new element. According to the sages, the first גם meant that although Moses was such a superior judge, others, less competent would also have to be appointed, whereas the second גם meant that although the elders were numerous, even their number did not suffice to ensure that the litigation procedure would run smoothly and promptly. It is also possible that the words גם אתה included the people who would feel weary because of standing in line, waiting. Yitro added a second גם to tell Moses that even if he co-opted the seventy elders this would still be far short of what was needed.