God's word good for us

Under the topic "Absolute Truth" in chapter 11 of Knowing God, J. I. Packer explains how God's Word, which he calls "the index of reality", not only demonstrates the trustworthiness of God, but also does good for us as his children. 

God's commands are true. "All your commands are true" (Ps 119:151). Why are they so described? First, because they have stability and permanence as setting forth what God wants to see in human lives in every age; second, because they tell us the unchanging truth about our own nature. For this is part of the purpose of God's law: it gives us a working definition of true humanity. It shows us what we were made to be, and teaches us how to be truly human, and warns us against moral self-destruction. This is a matter of great importance, and one which calls for much consideration at the present time.

We are familiar with the thought that our bodies are like machines, needing the right routine of food, rest and exercise if they are to run efficiently, and liable, if filled up with the wrong fuel -- alcohol, drugs, poison -- to lose their power of healthy functioning and ultimately to "seize up" entirely in physical death. What we are, perhaps, slower to grasp is that God wishes us to think of our souls in a similar way. As rational persons, we were made to bear God's moral image that is, our souls were made to "run" on the practice of worship, law-keeping, truthfulness, honesty, discipline, self-control, and service to God and our fellows. If we abandon these practices, not only do we incur guilt before God; we also progressively destroy our own souls. Conscience atrophies, the sense of shame dries up, one's capacity for truthfulness, loyalty and honesty is eaten away, one's character disintegrates. One not only becomes desperately miserable; one is steadily being dehumanized. This is one aspect of spiritual death. Richard Baxter was right to formulate the alternatives as "A Saint -- or a Brute”: that, ultimately, is the only choice, and everyone, sooner or later, consciously or unconsciously opts for one or the other. 

Nowadays some will maintain, in the name of humanism, that "Puritan" sexual morality of the Bible is inimical to the attainment of true human maturity, and that a little more license makes for richer living. Of this ideology we would only say that the proper name for it is not humanism but brutism. Sexual laxity does not make you more human, but less so; it brutalizes you and tears your soul to pieces. The same is true wherever any of God's commandments are disregarded. We are only living truly human lives just so far as we are laboring to keep God's commandments; no further. 

-- J. I. Packer, Knowing God, pp 113-14.