It is theological, but understandable and practical as well. Theology is always practical, something we often forget (sometimes because we would rather be intellectually lazy and pretend that the important things are "easy" and "simple"). But gifted theologians like Packer don't let us forget.
I have printed a particularly convicting passage from his book below.
"Self Centered Godliness. Modern Christians tend to make
satisfaction their religion. We show much more concern for self-fulfillment than for pleasing God. Typical of Christianity today, at any rate in the English-speaking world, is its massive rash of how-to books for believers, directing us to more successful relationships, more joy in sex, becoming
more of a person, realizing our possibilities, getting more excitement each day, reducing our weight, improving our diet, managing our money, licking our families into happier shape, and what not.
"For people whose prime passion is to glorify God, these are doubtless legitimate concerns; but the how-to books regularly explore them in a self-absorbed way that treats our enjoyment of life rather than the glory of God
as the center of interest. Granted, they spread a thin layer of Bible teaching over the mixture of popular psychology and common sense they offer, but their overall approach clearly reflects the narcissism--"selfism" or "me-ism" as it is sometimes called--that is the way of the world in the modern West.
"Now self-absorption, however religious in its cast of mind, is the opposite of holiness. Holiness means godliness, and godliness is rooted in God-centeredness, and those who think of God as existing for their benefit rather than of themselves as existing for his praise do not qualify as holy men and women. Their mind-set has to be described in very different terms. It is an ungodly sort of godliness that has self at its center" (taken from Keep in Step with the Spirit, pg. 82).
May the Lord enable us to do all to the glory of God (1 Cor. 10:31).