"The Tribe of Levi"

At that time יהוה set apart the tribe of Levi to carry the Ark of יהוה’s Covenant, to stand in attendance upon יהוה, and to bless in God’s name, as is still the case. That is why Levi has received no hereditary portion along with its kin: יהוה is its portion, as your God יהוה spoke concerning it.

Then the officials shall address the troops, as follows: “Is there anyone who has built a new house but has not dedicated it? Let him go back to his home, lest he die in battle and another dedicate it. Is there anyone who has planted a vineyard but has never harvested it? Let him go back to his home, lest he die in battle and another harvest it. Is there anyone who has paid the bride-price for a wife, but who has not yet taken her [into his household]? Let him go back to his home, lest he die in battle and another take her [into his household as his wife].” The officials shall go on addressing the troops and say, “Is there anyone afraid and disheartened? Let him go back to his home, lest the courage of his comrades flag like his.” When the officials have finished addressing the troops, army commanders shall assume command of the troops.

And Issachar’s chiefs were with Deborah;
As Barak, so was Issachar—
Rushing after him into the valley.
Among the clans of Reuben
Were great decisions of heart. Why then did you stay among the sheepfolds
And listen as they pipe for the flocks?
Among the clans of Reuben
Were great searchings of heart!

Deborah addresses Reuben directly: Why did you sit between the sheepfolds, in the pastures, hearing the bleating of the flocks? You are a tribe of shepherds living in tranquility in a land devoid of the sounds of war; the only sound you wish to hear is the whistling for the gathering of the flock. Among the divisions, or the divided hearts, or the exceptionally wise, of Reuben are great consultations of the heart. The prophetess mocks the tribe of Reuben’s decision to sit quietly in their place and remain neutral.

Why did you stay among the sheepfolds: That is to say, if you answer that you are frightened to come down to war, to face weaponry - if so, why at first did you settle the holding on the other side of the Jordan, between the border of the Land of Israel and the border of the nations? Is that not a dangerous place? So why did you choose to settle on this border?

After these individuals depart from the battlefront, the army is arrayed again and commanding officers are appointed at the head of the nation.
Powerful officers with iron axes in their hands are placed in the rear of each array of troops. If a person wants to leave the battle, they have permission to chop off his legs, for flight is the beginning of defeat.
In which instances are the above-mentioned individuals sent away from the battlefront? In a milchemet hareshut. By contrast, in a milchemet mitzvah, the entire nation must go out to war, even a groom from his chamber, and a bride from her pavilion.

Why did the Levites not receive a portion in the inheritance of Eretz Yisrael and in the spoils of war like their brethren? Because they were set aside to serve God and minister unto Him and to instruct people at large in His just paths and righteous judgments, as [Deuteronomy 33:10] states: "They will teach Your judgments to Jacob and Your Torah to Israel." Therefore they were set apart from the ways of the world. They do not wage war like the remainder of the Jewish people, nor do they receive an inheritance, nor do they acquire for themselves through their physical power. Instead, they are God's legion, as [ibid.:11]: states: "God has blessed His legion" and He provides for them, as [Numbers 18:20] states: "I am your portion and your inheritance."

Not only the tribe of Levi, but any one of the inhabitants of the world whose spirit generously motivates him and he understands with his wisdom to set himself aside and stand before God to serve Him and minister to Him and to know God, proceeding justly as God made him, removing from his neck the yoke of the many reckonings which people seek, he is sanctified as holy of holies. God will be His portion and heritage forever and will provide what is sufficient for him in this world like He provides for the priests and the Levites. And thus David declared [Psalms 16:5]: "God is the lot of my portion; You are my cup, You support my lot."
Blessed be the Merciful One who provides assistance.

Rav Yosef said that with regard to a mitzva, at the time when one is engaged in its performance it protects one from misfortune and saves one from the evil inclination; at the time when one is not engaged in its performance, it protects one from misfortune but it does not save one from the evil inclination. With regard to Torah study, both at the time when one is engaged in it and at the time when one is not engaged in it, it protects one from misfortune and saves one from the evil inclination.

Rabba objects to this explanation: If that is so, then with regard to Doeg (see I Samuel, chapters 21–22) and Ahithophel (see II Samuel, chapter 16), who were both wise scholars despite their wickedness, did they not engage in the study of Torah? Why did it not protect them from sinning? Rather, Rava said: With regard to Torah study, at the time when one is engaged in it, it protects and saves; at the time when one is not engaged in it, it protects one from misfortune but it does not save one from the evil inclination. With regard to a mitzva, both at the time when one is engaged in its performance and at the time when one is not engaged in its performance, it protects one from misfortune but it does not save one from the evil inclination.