Why did Moshe see fit to beseech Yisro not to leave them, when he begged him "Al Na Ta'azov osanu"?
Rashi: So that people should not say that Yisro only converted in order to receive a portion in Eretz Yisrael, and when he discovered that he would not receive one, he left them.
Seforno: Moshe was asking Yisro at least to let his sons accompany them.
What did Moshe mean when he said to Yisro "Ki al-Kein Yada'ata Chanoseinu ba'Midbar"?
Rashi: He was telling him that, since 1 he (Yisro) was acquainted with all their travels in the desert, it would be appropriate for him to remain with them and not to abandon them.
Seforno: Having seen up close Hashem's relationship with Yisrael, if he severs connections with Yisrael completely, 2 he will create a Chilul Hashem, inasmuch as people will say that had he seen true G-dliness, he would not have abandoned them together with his children.
Rashbam: He meant to say that Yisro took to heart their camping in the desert and acted as their advisor as the Pasuk describes at the beginning of Yisro. 3
And what did he mean when he concluded "Vehayisa lanu le'Einayim"?
Rashi #1 (citing Targum Onkelos): With reference to the previous phrase, it means that he had seen with his own eyes the miracles and mighty deeds that Hashem performed with Yisrael.
Rashi #3: He meant that if he remained with them, he would be dear to the like the pupil of his eye. 3