Relying totally on bitachon and avoiding the world is not G-d's desire

 Rav Saadiya Gaon (Emuna V’De’os 10:15): Many people say that it is best to totally devote oneself to serving G-d. They view the ideal as to fast during the day and get up at night to praise and give thanks to G-d. In other words they believe that one should withdraw from the world and assume that G-d will provide sustenance, medicine and all other mundane needs. Despite the fact that serving G-d brings great pleasure…, nevertheless an objection must be raised against this approach. The problem is that they advocate exclusive devotion to this activity and not to be engaged in any other. In fact if a person doesn’t concern himself about food his body will not survive. If he weren’t concerned about having children, then that would end all service of G-d. That is because if everyone agreed to this approach, eventually there would be no people left to worship G-d. In fact serving G-d involves parents and their children and grandchildren (Devarim 6:2). Furthermore let me explain the critical issue which has eluded these people. We are obligated to serve G d with all the commandments - both the rational one and the religious statutes (Devarim 10:12–13). How can a hermit fulfill the commandments concerning honest weights and measures (Vayikra 19:36)? How can he fulfill the commandments concerning unbiased judging of civil disputes (Devarim 16:19)? What opportunity does he have to fulfill the commandments concerning what is permitted and forbidden concerning eating meat and the like?…What opportunity does he have to keep the laws of impurity and purity…? Similarly, one can ask about agricultural laws, ma’aser, oaths, charity and other such laws. Perhaps you might argue that it is sufficient that these righteous hermits learn Torah to instruct others how to keep the commandments? However, that would not solve the problem since it would the students who would fulfill the commandments and not the teachers. Furthermore, regarding their assertion that one should have bitachon (trust) that G-d will take of their mundane needs - that is definitely true. However, they are ignoring a critical factor in bitachon. G-d has established the manner in which one attains his needs. If these righteous hermits applied their concept of bitachon to everything - than they logically should have bitachon that G-d will provide for their spiritual needs and should attain the reward in the World to Come without doing the Divine service! Since it is agreed that it is impossible to acquire the spiritual perfection without the Divine worship it is also impossible without being involved in the world and working, getting married and other activities which can perfect man. While it is true that sometimes G-d does take of these things in a miraculous manner without man’s efforts - it is not the normal practice that He changes the order of nature.