It states (14:24) עִמּוֹ אַחֶרֶת ַרוּח ה ָיְתָה עֵקֶב כָלֵב וְע ַבְדִּי ׁ ֶנָּהיוֹרִש וְזַרְעוֹ שָׁמ ָּה בָּא ֶׁראֲש הָאָרֶץ אֶל וַה ֲבִיאֹתִיו אַחֲרָי וַיְמ ַלֵּא, "My servant Kalev, because a different spirit was with him, and he followed Me wholeheartedly, I shall bring him to the Land to which he came, and his offspring shall possess it." Rashi writes that this means his offspring will inherit Chevron.
Kalev earned this great reward because he told the nation that they will succeed to conquer Eretz Yisrael, as it states (13:30) וַיַּהַס יָכוֹל כִּי ּאֹתָה וְיָרַשְׁ נוּ נַעֲלֶה ע ָלֹה וַיֹּאמֶר ֶׁהמֹש אֶל הָעָם אֶת כָּלֵב ּלָה נוּכַל, "Kalev silenced the nation toward Moshe and said, 'We shall surely ascend and conquer it, for we can surely do it!' " Reb Moshe Feinstein (Darash Moshe) zt'l explains that when Kalev told the nation that they would conquer Eretz Yisrael, they believed him. Kalev succeeded in bringing the nation to emunah. They all did teshuvah for a moment, and they believed that Hashem would bring them into Eretz Yisrael.
Their teshuvah didn't last long, because immediately afterwards, the Miraglim told the nation that they won't succeed and that they won't conquer the land, as it states (13:31) ח ָזָק כִּי הָעָם אֶל לַע ֲלוֹת נוּכַל לֹא אָמ ְ רוּ עִמּוֹ ע ָלוּ ֶׁראֲש וְהָא ֲנָשִׁים מִמ ֶּ נּוּ הוּא, "But the men who ascended with him said, 'We cannot ascend to that people for it is too strong for us!'" Klal Yisrael believed them, and once again, they cried and were afraid to go to Eretz Yisrael. Nevertheless, Kalev deserved immense reward because he brought the nation to teshuvah for a moment, and there is no limit to the value of teshuvah, even when it lasts just for a moment.
Reb Moshe Feinstein compares this idea to the halachah that it is permitted to be mechallel Shabbos to save a person's life, even if the chillul Shabbos will only grant the ill person one more moment to live (שעה חיי). A moment of life is so valuable that even chillul Shabbos is permitted. Similarly, a moment of teshuvah is immeasurable and extremely precious.
The Midrash (Bamidbar 16:2) states, "Kalev stood up on a bench and he said הס, and everyone was silent, prepared to listen to what he would say. Kalev said (14:7) הָאָרֶץ טוֹבָה מ ְאֹד מ ְאֹד, 'The land is very, very good.' Hakadosh Baruch Hu said to Moshe טובה לו מחזיק אני גדולה." Hashem said that He has hakaras hatov for Kalev, and promised to give him a great reward because Hashem had nachas ruach that Kalev said these words. The Midrash adds the pasuk (Devarim 1:36) זוּלָתִי יְפ ֻנֶּה בֶּן כָּלֵב, "except for Kalev..." and explains that זוּלָתִי means אִתִּי ל ָזֶה, "he was with Me, יוֹתֵר מ ִכֶּם רִבּוֹא ִּׁש ִּׁיםמִש, more than 600,000 Yidden." Specifically, Kalev was with Hashem. As we are explaining, this is because he brought the nation to teshuvah, although their teshuvah only lasted a few moments.
