The purpose of man’s creation in this world is only so that he will control his evil inclination, enjoy the fruits of his hard work in the world to come and merit to see the pleasantness of Hashem and visit his palace (for if Hashem would give him reward without any effort to control his inclination it would be an embarrassment for the person). If not for the evil inclination, a person would not be able to receive a reward, for he would be similar to the serving angels, and there would be no necessity for him to come to this world. Hakadosh Baruch Hu, however, formed man for His honor, for the honor of heaven is increased when a person controls his desires and does the will of his Maker, and this is a great pleasure for his Creator when people behave like mighty warriors to do His will. In direct proportion to the amount of work and effort and power of the evil inclination, so too will a man increase to make pleasure for his Creator and his reward will increase.
It is written in the Sefer Chasidim that for each commandment that a person’s inclination attacks him and tries to force him to rebel against the will of his Creator, if he controls the inclination, he will receive reward equivalent to that for a hundred commandments about which the inclination does not push him. This is the reason for the saying of Chazal that “In a place where people who have repented stand, completely righteous people will be unable to stand”, for the righteous people have less of an evil inclination compared to the people who have repented who were used to transgressing sins and find it extremely difficult to move away from them. Therefore, when they repent and overcome their desires, they cause great pleasure to their Creator and their reward is very great.
There are some who use this idea to explain the following saying of Chazal: “One who benefits from his own hard work is greater than one who has fear of heaven”, that it means to say that one who worked very hard to overcome and conquer his evil inclination and gets reward for it, is greater than one who is by nature one who fears G-d, as on who benefits from such work will have more reward in the next world.