From Ohr Avigdor Shaar Bitachon by Rabbi Avigdor Miller
Chovos Halevavos doesn’t want a person to feel that the bread he eats is tasteless, without pleasure. When he walks in the street and he sees the sunlight, he should not think it’s nothing. On the contrary, as was explained in the Shaar Habechinah, the true servant of Hashem sees the kindness in everything. He sees how Hashem has put wisdom and kindness into all forms of material existence. As it says, "His greatness and His goodness fill the world."
So when he eats whatever he eats, he certainly enjoys it and he thanks Hashem that it’s so pleasant to eat food. There is no question about that. So what is Chovos Halevavos trying to tell us with his discussion of abstinence?
Chovos Halevavos is teaching that a person should never become overly enthusiastic about any material aspect of his existence. For example, he should never go overboard about the function of eating. He should not fall in love with nature. True, he should see in nature and in the bread that he eats all the kindness of Hashem, but he shouldn’t become enthusiastic about anything that is only a means to an end.
Similarly, David Hamelech fought for the people of Yisrael, but it wasn’t because he loved war or he wanted to conquer other nations. He was a servant of Hashem. When people get into the spirit of military activities and become enthusiastic about the martial arts, it’s not called the service of Hashem. If people want to be authors and writers for the purpose of gaining renown, it’s not called the service of Hashem.
If a person has a family and becomes so enthusiastic about them that they are the center of his life, he ceases to be a servant of Hashem. True, Hashem wants him to have a family and raise children devoted to His service, as it says, "I have acquired a man for Hashem" (Bereishis 4:1). But He doesn’t want a man’s family to be his whole life.
Certainly a person should enjoy his children. That attitude is part of enjoying the kindness of Hashem, but he shouldn’t become like some people who live for their children. There are people who can’t live without their children. They are always traveling to see their children and be with them. That becomes their life.