וַיִּקְרָ֨א מֹשֶׁ֜ה לִֽיהוֹשֻׁ֗עַ וַיֹּ֨אמֶר אֵלָ֜יו לְעֵינֵ֣י כָל־יִשְׂרָאֵ֘ל חֲזַ֣ק וֶאֱמָץ֒ כִּ֣י אַתָּ֗ה תָּבוֹא֙ אֶת־הָעָ֣ם הַזֶּ֔ה אֶל־הָאָ֕רֶץ אֲשֶׁ֨ר נִשְׁבַּ֧ע יְהוָ֛ה לַאֲבֹתָ֖ם לָתֵ֣ת לָהֶ֑ם וְאַתָּ֖ה תַּנְחִילֶ֥נָּה אוֹתָֽם׃
E Moshe chamou a Yehoshua e lhe disse aos olhos de todo Yisrael: Fortalece-te e sê corajoso, pois tu entrarás com este povo na terra que o Eterno jurou a seus pais dar-lhes, e tu a farás herdar a eles.
Rashi
כי אתה תבוא את העם הזה — Translate this as the Targum does: ארי אתה תעול עם עמא הדין, THOU SHALT GO WITH THIS PEOPLE. Moses, by the statement “Thou shall go with this people” (as one of them) said in effect to Joshua: The elders of the generation will be with thee: everything has to be done according to their opinion and their advice. The Holy One, blessed be He, however, said to Joshua, (v. 23) “For thou shalt bring (תביא) the children of Israel into the land which I swore unto them” — thou shalt bring them even against their will; everything depends on you alone: if necessary take a stick and beat them over the head: there can be but one leader for a generation, and not two leaders for a generation (Sanhedrin 8a).
Chizkuni
לעיני כל ישראל, “in the sight of all of Israel;” this was necessary so that none of them would ever be able to say toJoshua that as long as Moses had been alive he had not had permission to assume the mantle of leadership.
Ibn Ezra
be courageous and brave to Joshua as well, because he was to be their leader.