This is a must read for all believers. It belongs on every Christian's bookshelf and the principles it offers belong in every believers heart. If you do hurry off to purchase a copy, and you're not accustomed to reading "latinized puritanical english" (as Packer calls it), I suggest that you buy the version that has been "made easy to read." Although, if you read it in it's original form, it will make you slow down and digest what he is saying. No matter what, the fact that Owen wrote it for teen-aged boys is flat out humbling.
Then entire book is based on half of Romans 8:13, "but if ye through the Spirit do mortify the deeds of the body, ye shall live." 176 pages dedicated to 1/2 a verse ain't to shabby. It is a most thorough evaluation of the Christian's efforts towards mortification (putting to death the sinful deeds of the flesh) and vivification (putting on the character and traits of Christ).
The overall thrust of the book is that we, as believers, have the Spirit of Christ in us who wages war against the fleshy deeds of the body. It is amazingly balanced in it's approach to practical and doctrinal Christianity. There is too much in it for me to give you an abridged outline so I'll tell you the thing that hit me the hardest.
Owen calls us to deep introspection throughout the entire book. But one of the things that he warns us against is hastily speaking peace to our conscience before the Lord speaks peace to it. So often we run to the cross immediately after we fall under conviction, and that is encouraged, but we do not stay at the cross long enough. We want immediate peace and rest for our conscience, so we don't stay at the foot of the cross long enough to really see the filth of our sin and realize the magnitude of it. The result is that we don't deal with it in it's entirety and we don't feel the weight of it. Thus, we will more rapidly fall into the same sin because the remedy works quickly and we don't feel the weight of our depravity. What does this problem call us to do? Spend more time in thought and reflection on the glorious wrath absorbing death of our Savior, the wrath that we deserve, which he appeased, in our stead, for the sins we commit (if you thought that was a long sentence with lots of commas, just read some Owen).
Every once and a while, Owen would write a short sentence that was loaded with glorious truth. Here are a few:
"the vigour, and power, and comfort of our spiritual life depend on the mortification of the deeds of the flesh."
"be killing sin, or it will be killing you."
"Sin always aims at the utmost: every time it rises up to tempt or entice, might it have it's course, it would go out to the utmost of it's kind." Meaning, a lustful glance, if it could have it's course, would result in adultery, and is a step towards it. That's serious.
'An unmortified lust will drink up the spirit and all the vigour of the soul, and weaken it for all it's duties."
"There is no death of sin, without the death of Christ." AMEN
"All attempts, then, for mortification of any lust, without an interest in Christ, are vain."
Those were just from the first 7 chapters. Read it slowly and enjoy.