Notes on the Bible, by Albert Barnes, [1834], at sacred-texts.com
The trumpet was a straight instrument, differing in this respect from the curved horn or cornet; and is represented, among the other spoils of the temple, on the Arch of Titus. See Exo 25:23 cut. From Egyptian monuments it appears that the Jewish trumpet was copied from that used in the armies of the Pharaohs. The cornet was at first a simple ram's horn Jos 6:4, and the metal instrument of later times preserved the original shape.
Blow an alarm - i. e. along continuous peal. Compare Num 10:7, ye shall blow, but not sound an alarm: i. e. blow in short, sharp notes, not in a continuous peal. A third and a fourth alarm were probably blown as signals.
The sons of Aaron - As the trumpets were emblematic of the voice of God, the priests only were to use them. At this time there were only two "sons of Aaron;" but in later times, when the number of priests was greater, more trumpets were used; we read of seven in the times of Joshua and David (see the marginal references.); and of a hundred and twenty in that of Solomon Ch2 5:12.
For examples of the employment of trumpets in war compare marginal references and Ch2 20:28. By employment of them was signified the dependence of God's people on His aid.
In the day of your gladness - Compare Num 29:1; Lev 23:24; Ch2 29:27; Ezr 3:10; Neh 12:35, Neh 12:41; Psa 81:3.
At this point commences the second great division of the book, extending to the close of Num. 14. The remaining verses of the present chapter narrate the actual break up of the camp at Sinai and the order of the march.
The wilderness of Paran - See Gen 14:6 note. The wilderness is mentioned here by anticipation. The earliest halting-places, Kibroth-hattaavah and Hazeroth, were not within its limits Num 11:35; Num 12:16.
Rather, And they journeyed (or, set forth) in the order of precedence according to (i. e. established by) the commandment of the Lord, etc., and described in Num 10:14-28.
According to their armies - Compare Num 1:3. There were three tribal hosts in each camp; and each tribe had of course its subdivisions.
A more precise determination of the method of executing the order given in Num 2:17. The appointed place of the tabernacle, in the midst of the host, was represented during the march by the ark, the holy vessels, etc. carried by the Kohathites. The actual structure of the tabernacle was borne in advance by the Gershonites and Merarites, immediately behind the camp of Judah; so as to be set up ready against the arrival of the sacred utensils borne by the Kohathites. Compare Num. 2; 4,
Hobab, the son of Raguel - Or Reuel Exo 2:18. Reuel was probably not identical with Jethro: and Hobab was the brother-in-law, not the father-in-law, of Moses; the Hebrew word translated in the King James Version "father-in-law," signifying simply any relation by marriage (Exo 3:1 note). Hobab Jdg 1:16; Jdg 4:11 eventually accompanied the Israelites and obtained a settlement with them in the land of Canaan. Hobab and Jethro may have been brethren and sons of Reuel.
Thou mayest be to us instead of eyes - A proverbial expression still in use in the East. Hobab would indicate the spots where water, fuel, and pasture might be found, or warn them of the dangers from hurricanes, and point out localities infested by robbers.
Three days' journey - Probably a technical expression for such a distance as could not be traversed in a single day, and therefore not without intervals of encampment and due provision: compare Gen 30:36; Exo 3:18; Exo 5:3; Exo 8:27; Exo 15:22. The technical use of the phrase "Sabbath-day's journey" for another average distance, Act 1:12, is similar.
The ark of the covenant of the Lord went before them - From Num 10:21; Num 2:17 it would appear that the usual place of the ark during the march was in the midst of the host. It was evidently an exceptional case when, in Jos 3:3, Jos 3:6, the ark preceded the people into the bed of the Jordan. Hence, the words "went before them" do not here imply local precedence. The phrase, or its equivalent, is used of a leader going out in command of his troops, Num 27:17; Deu 31:3; Sa1 18:16; Ch2 1:10; and similarly the ark may well be said to have gone at the head of the Israelites, when it was borne solemnly in the midst of them as the outward embodiment of the presence whose sovereign word was their law.
A resting place - literally, "rest." It is commonly understood of each successive encampment; or, in particular, of the first encampment. Yet the term would hardly be here employed, did it not carry with it a higher meaning, pointing to the promised rest of Canaan, for which the Israelites were now in full march, and from the speedy enjoyment of which no sentence of exclusion as yet debarred them. Compare the marginal references.
Each forward movement and each rest of the ark was made to bear a sacramental character. The one betokened the going forth of God against His enemies; the other, His gathering of His own people to Himself: the one was the pledge of victory, the other the earnest of repose.
Num 10:36 may be translated: "Restore" (i. e. to the land which their fathers sojourned in), "O Lord, the ten thousands of the thousands of Israel." (Compare Psa 85:4, where the verb in the Hebrew is the same.)