Numbers 13:16

Moshe called Hosheiah, etc. He prayed for him, ‘may Hashem save you from [joining] the counsel of the spies.”

These are the names of the men whom Mosheh sent to explore the land; and when Mosheh saw his humility, he called Hoshea bar Nun Jehoshua.

ויקרא משה להושע בן נון יהושע, this does not mean that the people from then on called this man Joshua. It means that the man who had been referred to as Hosheah son of Nun in his father’s house was the one whom Moses now referred to as Joshua. The change had occurred already at the time when Moses appointed this man to be his personal valet. It was customary to change the names of people who were promoted in rank. We find this the first time when Pharaoh changed Joseph’s name to Tzofnat Paneach (Genesis 41,45) We find it again in Daniel 1,6 when Nevuchadnezzar’s chief officer changed Daniel’s name to Belteshazzar. This had been a reference to a Babylonian idol so named. The first time Joshua’s name had been changed was in Exodus 24,13.

ויקרא משה להושע בן נון יהושע, the Torah means that this man was known as a man of valour by the name of Hosheah among the members of his tribe. The fact that he has been referred to as “Joshua” already in Numbers 11,28 is because in his capacity as Moses’ personal valet Moses had changed his name in the form of a prayer asking that he be the instrument of his own salvation and that of others.

ויקרא משה להושע בן נון יהושע, “Moses called (changed) the name of Hoshea to Yehoshua son of Nun. The Midrash Tanchuma, section 6 on this portion, in dealing with this change of name, writes as follows: “what prompted Moses to change the name of Hoshea to Y’hoshua by adding the letter י (equivalent the number ten) to his name? Moses foresaw that Calev, another spy who did receive his ancestral share in the Holy Land received one share, as detailed in the Book of Judges 1,20, seeing he had bothered to make a special detour at Chevron (Numbers 13,22) (“he,” sing. came to Chevron) whereas Joshua, who would lead the people to the Land and conquer it, received ten shares, this was hinted at by the change of his name. [Seeing that Joshua personally did not have any children, looking at the matter technically, although his tribe of Ephrayim, did of course receive their share, perhaps Moses wanted to indicate that he in fact, at least, in the spiritual sense of the word, “inherited” the 10 shares of the Holy Land, that would have become the shares of the other ten spies had they not slandered the land. Ed.] According to the Talmud Yerushalmi tractate Sanhedrin, chapter 2, halachah 6, by adding the letter י at the beginning of his name, so that it began with the two letters spelling the name of G–d, Moses hoped to arm him spiritually against becoming spiritually contaminated by the other ten spies. When Sarah’s name שרי had been changed to שרה, she had lost a letter, i.e. the letter י. Joshua now received this letter. Avraham had the letter ה she had lost, added to his name when that was changed from אברם to אברהם. [Seeing that they both no longer needed these two letters, having died long ago, they were used by Moses as helping Joshua to withstand the brainwashing by the ten spies. Ed.]