1 Peter 1:13-16
In these our texts today, Peter contrasts the thinking and living of the scattered Christians, in contrast with their former lives as heathen. He shows that Christians are to live distinctly different lives from the heathen; and in fact shows that the distinct differences of the Christians are in themselves a tremendous and compelling gospel invitation to the heathen, who observe the lives of the Christian and wonder at it.
Thus we must immediately point out that Christians must not negatively portray the Christian life among the heathen. At the heart of it, by merit of his genuine relationship with God, the Christian possesses what the godless heathen deeply desires. So the Christian who does not whole-heartedly embrace the deep meaning of his Christianity; the Christian who is fundamentally in conflict with his own Christianity; may very likely not be a Christian at all.