I have found myself time and time again going back to Challies’ book as I attempt to by God’s grace think more strategically about mortifying sin and walking in the freedom that Christ guards, keeps and has won for us.  I hope you will do yourself a great service and purchase the book, rather than merely being dependent upon my meager attempt at summarizing his words (after all they’re his words not mine!).

Chapter 4 of Challies’ book is about the gifts of sex.  Here is a paragraph worth mentioning that describes the goodness of sex: “we do not know how long it was before God formed Eve, but we do know that for a time, Adam lived a life of celibacy.  And during this time, he joined with God in the search for a suitable mate.  God said, ‘it is not good that the man should be alone; I will make him a helper fit for him’ (Genesis 2:18).  And yet he did not make this helped immediately.  Instead, he brought Adam every living creature, one by one.  And in all of creation there was no helper for Adam, no mate suitable to him.  Through all this time Adam waited patiently, he waited perfectly, sinlessly trusting in God’s provision.  Was Eden flawed in the absence of sex and marriage?  Not at all!  It would just be better with them for, in the words of God, for it was not good for this man to be alone” (Challies, pp. 47-48).

Challies states four gifts of sex:

1. Sex is good.  It is good for no other reason than it was created by God.
2. Sex motivates joyful obedience. “It’s good that we want to have sex.  God made it that way.  God made sex for marriage and marriage for sex.  Sexual desires motivates a man (in part) to pursue a wife and marry her so that together they can enjoy sex. This same desire motivates a man (in part) to keep pursing his wife even after they are married” (Challies, pp. 52).
3. Sex strengthens a husband’s leadership.  The desire for sex is typically not given in equal measure.  “It is typically given in greater part to men.  Why is this?  The answer, I’m convinced, goes right to the heart of the husband-wife relationship.  God commands that men, husbands, be leaders.  Men are to take the leading role while women are to follow.  God intends that men take leadership even in sex, and, therefore, he gives men a greater desire for sex” (Challies, pp. 53).
4. Sex enhances true freedom.  Sex is intended by God to be alluring and even captivating.  It is meant to put a powerful emotional seal on marriage…” (Challies, pp. 55).

Some points of application:

1. Sex is to be between a husband and a wife.
2. Sex is to be done with self-control and done in love, selflessness, not in anger.
3. Sex should not be part of a couple’s relationship until the appropriate time of marriage.
4. Sex is to be a regular part of the landscape of a couple’s marriage.
5. Sex takes work. 
6. Sex is intimately connected with all other facets of a couple’s marriage.