Beloved, I beg you as foreigners and pilgrims, to abstain from fleshly lusts, which war against the soul;
Abstain from fleshly lusts, which war against the soul ...  There ar two reasons assigned in this verse to support the renunciation of fleshly lusts: (1) the readers are sojourners, and (2) the lusts make war against the soul.  The metaphor of warfare is an apt one for the Christian life. That life is a constant struggle against many enemies, both within and without.  The social order itself is basically hostile to Christianity, and the inward desires of the flesh and of the mind also constantly tend to erode spirituality.