Numbers 27:19

And command him. Concerning the Bnei Yisroel. Know that they are tedious and recalcitrant — [your appointment is] on condition that you accept this.

and make him stand before Elazar the priest and the whole congregation, and instruct him in their presence.

AND THOU SHALT COMMAND HIM [Joshua] — “concerning Israel, [saying to him]: ‘Know that they are troublesome, that they are stubborn. [Accept this position of leadership over them with full awareness of this and] on condition that you take upon yourself [all this].’” This is the language of Rashi. But it is not correct in my opinion, because it says [and thou shalt command him] before their eyes [and Moses would not have told Joshua to say such words in their presence], for this matter ought rather to have been told to him [Joshua] between the two of them [Moses and Joshua]; for if he would say it in their presence, it would [only] have caused them to break off all restraint. And it would have been more fitting that he [Moses] should chastise the people, warning them separately [and not in Joshua’s presence] not to be troublesome and stubborn any more [rather than to tell Joshua, in their presence, that they were a troublesome and stubborn people]! But [the meaning of] and thou shalt command him before their eyes is that you should instruct him in the duties of a prince and judge, since it was because he [Joshua] was to be their leader that he entrusted them to his care. [Therefore] he should [indeed] have warned him to exert himself exceedingly on their behalf, and to fight the battles of the Eternal, and that he should be the one to go out before them [in battle] and to bring them in, and that he should be careful in matters of judgment. These [instructions] indeed ought to be said in their presence, in order that they should trust him and listen to him, for they would then know that he will treat their affairs in a truthful manner, since his master had so commanded him. And this is what Moses [actually] did, as it is said there, And Moses called unto Joshua, and said unto him in the sight of all Israel: ‘Be strong and of good courage etc. fear not, neither be dismayed.’ And in the Sifre [we find the following text]: “And command Joshua — concerning instruction [learning and teaching Torah]. And encourage ‘him,’ and strengthen ‘him.’ This teaches us that there cannot be two leaders in one generation.” Now these are duties of the prince, to be firm and not to be afraid of the people.
In my opinion the plain meaning of Scripture is that the explanation of [the expression] ‘v’tzav’ (and thou shalt command) him before their eyes is [that it refers to] appointing [him officially as their leader], for Moses was to appoint Joshua in the presence of the people to be the ruler over them. This is similar to [the expression], from the time ‘tzivah othi’ (I was appointed) to be their governor etc. So also: ‘vayetzaveihu’ (and the Eternal hath appointed him) to be the prince over His people. Similarly, Even from the day that ‘tzivithi’(‘I commanded’) judges to be over My people Israel, which means “I appointed” [and likewise all these expressions of ‘tzav,’ which literally mean “command,” here mean “appoint”].

וצויתה אותו לעיניהם, you appoint him as leader in their very presence so that they will accept his authority willingly and will be obedient to his directives. The expression צווי meaning appointment is not unique; we find it in Samuel I 25,30 וצוך לנגיד, “He will appoint you as leader.” (Avigail speaking to David) We find it also in Samuel II 7,11 למן היום אשר צוותי שופטים, “from the day I have appointed Judges, etc.” (G’d giving a message to the prophet Nathan for David)