וַיִּהְי֣וּ פְקֻדֵיהֶ֗ם שְׁלֹשָׁ֤ה וְעֶשְׂרִים֙ אֶ֔לֶף כָּל־זָכָ֖ר מִבֶּן־חֹ֣דֶשׁ וָמָ֑עְלָה כִּ֣י ׀ לֹ֣א הָתְפָּקְד֗וּ בְּתוֹךְ֙ בְּנֵ֣י יִשְׂרָאֵ֔ל כִּ֠י לֹא־נִתַּ֤ן לָהֶם֙ נַחֲלָ֔ה בְּת֖וֹךְ בְּנֵ֥י יִשְׂרָאֵֽל׃
А их насчитывалось двадцать три тысячи человек каждый в возрасте от месяца и выше; потому что они не были причислены к детям Израилевым, потому что не было уделено им наследство среди детей Израилевых.
Rashi
כי לא התפקדו בתוך בני ישראל FOR THEY WERE NOT NUMBERED AMONGST THE CHILDREN OF ISRAEL, that they should also be numbered from twenty years old and upwards. What was the reason that they were not numbered from twenty years old? כי לא נתן להם נחלה BECAUSE NO INHERITANCE WAS TO BE GIVEN THEM, while those who were counted from twenty years old were persons who were recipients of an inheritance, as it is said, (v. 54) “to everyone shall his inheritance be given according to those that were numbered of them”, (consequently the Levites had to form a different group for the census).
Rabbeinu Bahya
ויהיו פקודיהם שלשה ועשרים אלף כל זכר מבן חדש ומעלה, “and the number of enrolled ones comprising all those from one month and up was 23,000.” I have explained on Numbers 4,49 why the Levites were counted from one month and up.
Chizkuni
שלשה ועשרים אלף, “twenty three thousand.” According to Bamidbar Rabbah 5,1 the Levites who carried the Holy Ark suffered losses in their numbers due to flashes of lightning emanating from that Ark from time to time.[This editor presumes that what is implied it is that not all the Levites all the time when engaged in that task had their minds on their holy task as they should have had. Or, seeing that the Levites had been counted not from the age of 20, but from the age of only one month, a number might have succumbed to sickness before they were strong enough. The number of adult Israelites involved in the census had hardly changed.