(יז) וַיִּשְׁלַ֤ח אֹתָם֙ מֹשֶׁ֔ה לָת֖וּר אֶת־אֶ֣רֶץ כְּנָ֑עַן וַיֹּ֣אמֶר אֲלֵהֶ֗ם עֲל֥וּ זֶה֙ בַּנֶּ֔גֶב וַעֲלִיתֶ֖ם אֶת־הָהָֽר׃ (יח) וּרְאִיתֶ֥ם אֶת־הָאָ֖רֶץ מַה־הִ֑וא וְאֶת־הָעָם֙ הַיֹּשֵׁ֣ב עָלֶ֔יהָ הֶחָזָ֥ק הוּא֙ הֲרָפֶ֔ה הַמְעַ֥ט ה֖וּא אִם־רָֽב׃ (יט) וּמָ֣ה הָאָ֗רֶץ אֲשֶׁר־הוּא֙ יֹשֵׁ֣ב בָּ֔הּ הֲטוֹבָ֥ה הִ֖וא אִם־רָעָ֑ה וּמָ֣ה הֶֽעָרִ֗ים אֲשֶׁר־הוּא֙ יוֹשֵׁ֣ב בָּהֵ֔נָּה הַבְּמַֽחֲנִ֖ים אִ֥ם בְּמִבְצָרִֽים׃ (כ) וּמָ֣ה הָ֠אָרֶץ הַשְּׁמֵנָ֨ה הִ֜וא אִם־רָזָ֗ה הֲיֵֽשׁ־בָּ֥הּ עֵץ֙ אִם־אַ֔יִן וְהִ֨תְחַזַּקְתֶּ֔ם וּלְקַחְתֶּ֖ם מִפְּרִ֣י הָאָ֑רֶץ וְהַ֨יָּמִ֔ים יְמֵ֖י בִּכּוּרֵ֥י עֲנָבִֽים׃
(17) When Moses sent them to scout the land of Canaan, he said to them, “Go up there into the Negeb and on into the hill country, (18) and see what kind of country it is. Are the people who dwell in it strong or weak, few or many? (19) Is the country in which they dwell good or bad? Are the towns they live in open or fortified? (20) Is the soil rich or poor? Is it wooded or not? And take pains to bring back some of the fruit of the land.”—Now it happened to be the season of the first ripe grapes.
Put forth strength, use one's strength (i.e. he exerted himself, he sat up by great effort), as in Gen 48:2
Brown Driver Briggs Dictionary, p. 305
Now when Moshe sent them to scout out the land of Canaan,
he said to them:
Go up this (way) through the Negev/Parched-Land,
and (then) you are to go up into the hill-country.
And see the land--what it is (like),
and the population that is settled in it:
are they strong or weak,
are they few or many;
and what the land is (like), where they are settled:
is it good or ill;
and what are the towns are (like), where they are settled therein:
are (they) encampments or fortified-places;
and what the land is (like):
is it fat or lean,
are there in it trees, or not?
Now exert yourselves,
and take (some) of the fruit of the land
--now these days (are) the days of the first ripe-grapes.
The Schocken Bible: Volume 1, The Five Books of Moses, Everett Fox, p. 722
And Moses sent them to scout the land of Canaan, and he said to them, "Go up this way through the Negeb, and you shall go up into the high country. And you shall see the land, what is it like, and the people that dwells in it, are they strong or slack, are they few or many. And what is the land in which they dwell, is it good or bad, and what are the towns in which they dwell, are they in open settlements or in fortresses. And what is the land, is it fat or lean, are there trees in it or not. And you shall muster strength and take of the fruit of the land." And the season was the season of the first ripe grapes.
The Five Books of Moses, Robert Alter, p. 746
Robert Alter commentary on Num. 13:20 "muster strength and take of the fruit of the land. The notion that strength is required to take a sample of the fruit of the land is the first hint that the fruit is preternaturally heavy, just as the inhabitants are preternaturally large. The hyperbolic--or legendary--indication in verse 23 is that a single cluster of grapes is so heavy that it requires two men to carry it."