Midrash su Deuteronomio 20:4

"But ye, ye are not so, whereas (Deut. 20, 4) For the Lord your God, It is who goeth with you, etc. This refers to the camp containing the Holy Ark." And why so much? Because the Holy Scroll with all its accompanied things was placed in the ark. (Fol. 43) Similar to this says the passage (Num. 31, 6) And Moses sent them a thousand of each tribe to the army. This refers to the Sanhedrian; and Phinehas, this refers to the anointed priest as the chaplain of the army! with the Holy vessels, this refers to the ark and the tables; and the trumpets for blowing the alarm, these are the hornets. We are taught in a Baraitha: Phinehas did not go in rain into that war, but to pay off the judgment of his mother's father, concerning whom it is said (Gen. 37, 36) And the Medionites sold him into Egypt. Do you mean to say that Phinehas is a descendant of Joseph? Behold, there is a passage (Ex. 6, 26) And Elazar, the son of Aaron took himself one of the daughters of Putiel, for a wife. Does not the word Putiel refer to a descend of Jethro, who fattened calves for sacrificing unto idols. [Hence he was a descendant of Jethro and not of Joseph?] Nay the word Putiel refers to Joseph who [is surnamed Putiel because he] conquered his evil inclination. But were not tribes disgracing Phinehas saying to him: "Look at the son of Putti whose mother's father fattened calves to the sacrifice of the idols, should he execute a prince of the tribe of Israel," [hence he is a descendant of Jethro? We must therefore say that if his mother's father was a descendant of Joseph then his mother's mother was of the lineage of Jethro, and if his mother's mother was a descendant of Joseph then his mother's father was of the lineage of Jethro, [hence he was thus a descendant of both.] This may also be inferred from the above passage which is written, one of the daughters (plural) of Putiel, which refers to two names. The inference is finally sustained.

(Devarim 20:4) "For it is the L-rd your G-d who goes with you to do battle with your foes": He who was with you in the desert will be with you at this time.