Matthew Poole and continuators on Numbers 31:6

6 And Moses sent them to the war, a thousand of every tribe; them and Phinehas the son of Eleazar the Priest to the war, with the holy instruments , and the trumpets to blow in his hand.

Who had the charge not of the Army, as General, (an Office never committed to any Priest in all the Old Testament) but of the Holy Instruments, &c. as is here expressed, and was also sent to encourage, and quicken, and confirm them in their good enterprize. It is not here mentioned who was the general, whether Iosua, as some think, because he is not named amongst those who went out to meet the returning host, though that might be for other reasons, or some other Prince, nor is it worth while to determine.

Either 1. the Ark, with the things belonging to it, which before the building of the Temple, they did sometimes carry into the War for the encouragement of their Army. See Numb. 14. 44. Ios. 6. 9. 1 Sam. 4. 4. and 14. 18. But why then is it thus ambiguously expressed, seeing in all the other places it is called by its proper Name? Nor is the Ark ever so called in Scripture. Or 2. The Trumpets, as it here follows, the words being thus to be read, the Holy Instruments, that is, the Trumpets: for and is oft times put exegetically for that is, or to wit, as Gen. 13. 15. 1 Chron. 21. 12. compared with 2 Sam. 24. 13. Zach. 1. 4. and 9. 9, &c. Or rather 3. The Holy Breast-plate, wherein was the Urim and Thummim, which was easily carryed, and used, and very useful in War upon many emergent occasions. See 1 Sam. 23. 9. and 30. 7.

Which were to be used in war as well as in the service of the Tabernacle. See Numb. 10. 9. 2 Chron. 13. 12.