Some causes of spiritual decline and death - An excerpt from J. I. Packer

I was reading J.I. Packer's Knowing God and came upon his paragraph. To me this description explains how spiritual death takes a hold in our lives. Even though we may be a believer and have eternal life, God says that sin works death in us somehow. I think this helps to frame my thinking on the subject.

 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 de-humanised. This is one aspect of spiritual death.

Knowing God, J.I. Packer; InterVarsity Press, Illinois, 1973; Page 102-103