Rambam (Hilchos Shemitta 13:12–13): Why didn’t the tribe of Levi merit an inheritance in the land of Israel as well as the spoils of war like the other tribes? It is because they were given the responsibility to serve G d and to teach His righteous ways to the masses… Therefore they were separated from the ways of world and were not involved in war like the rest of Israel and they neither inherited nor obtained things by means of physical endeavors. They were G d’s army and G d provided for them. However, this way of life is not exclusively for the tribe of Levi but in fact any person in the world whose spirit moves him. He understands by himself to separate and stand before G d to serve Him in order to know G d. If he goes in the upright path, as G d desired then the yoke of constant worry characteristic of mankind will be taken from him. He will be sanctified, as holy of holies and G d will be his portion and inheritance forever. He will consequently obtain in this world that which he needs in the same way as the Cohanim and Leviim…
Rambam (Torah Study 03:10) Anyone who comes to the conclusion that he should involve himself in Torah study without doing work and derive his livelihood from charity, desecrates G-d's name, dishonors the Torah, extinguishes the light of faith, brings evil upon himself, and forfeits the life of the world to come, for it is forbidden to derive benefit from the words of Torah in this world.
Rambam (Torah Study 03:10) "Whoever benefits from the words of Torah forfeits his life in the world." Also, they commanded and declared: "Do not make them a crown to magnify oneself, nor an axe to chop with." Also, they commanded and declared: "Love work and despise Rabbinic positions." All Torah that is not accompanied by work will eventually be negated and lead to sin. Ultimately, such a person will steal from others.
Rambam (Torah Study 03:11) It is a tremendous advantage for a person to derive his livelihood from his own efforts. This attribute was possessed by the pious of the early generations. In this manner, one will merit all [types of] honor and benefit in this world and in the world to come, as [Psalms 128:2] states: "If you eat the toil of your hands, you will be happy and it will be good for you." "You will be happy" - in this world. "It will be good for you" - in the world to come, which is entirely good.