I have returned to my garden, my sister, my bride.
— Song of Songs
I have read an interesting idea from a sicho on parshas Lech Lecha this Shabbos.
The episode of Avraham Avinu and Sara descending to Egypt is well known. During their crossing the Nile river, Avraham told Sara that she should pretend to be his sister, lest she is seized by the immoral Egyptians and he is killed, chv"sh.
On a spiritual level, parshas Lech Lecha (whose main theme is the journey of Avraham Avinu to Eretz Yisroel from the place of his birth) is a metaphor for the soul's journey from the upper worlds to this world.
The concept of "sister" represents the soul; the concept of "wife" represents the body. (In this case, Avraham Avinu represents the essence of the soul, cheilek Elokah mima'al mamosh, yechida shebenefesh.)
The soul's relationship with Hashem is natural, like that of a sister and a brother (while a sister and a brother may get in a fight, it is only under extreme circumstances that they will lose all relationship, G-d fobid). The relationship of the body with Hashem is that of a wife with a husband. The relationship at first is not "natural" (in the sense that a newlywed couple have to grow accustomed to each other and when they just meet are strangers); thus, if it is not cultivated properly, it can fall apart, chv"sh. On the other hand, if it is nurtured and grows, the relationship between a husband and a wife can become much more explosive and stronger than that between siblings can ever hope to be.
This is the lesson for our avoidas Hashem. When our soul enters this world (similar to how Avraham descended into Egypt), it is in a state of weakness. It must be on guard against the foreign and potentially destructive elements of the material. Therefore, it must rely on its "natural" relationship with Hashem — similar to that of siblings, a relationship which is the result of the soul's origins. That is why the beginning of the soul's life in this world (the childhood and youth), as well as the times of special spiritual closeness to Hashem (Shabbos and holidays) must be spent with the focus on study of Torah and davening. (Also, of course, the soul must renew and strengthen its connection with Hashem on a daily basis by learning and davening at set times.)
On the other hand, the whole purpose of the soul's descent is to elevate its relationship with Hashem to a completely new level. That can only be accomplished by becoming Hashem's "wife" — by using the body to do the mitzvos that transform the world into a dwelling place for Hashem (similar to how a wife transforms an empty and cold basement apartment into a home for her husband). That is why one cannot spend all his time only learning and must also do mitzvos and interact with the world for the purpose of making it holy.
I also think, on a deeper level, that although one must originally shy away from those things that interest the body (I do not just mean bodily pleasures; I mean, more generally, the pleasures of this world, including the aesthetic and intellectual ones), eventually, it is one's purpose in this world to connect the explosive nature of these endeavors with holiness.