In my sermon on the seventh commandment, “You shall not commit adultery,” I focused on “adultery of the heart.” I said that I wanted to focus on this kind of adultery—the kind that Jimmy Carter famously confessed to in a 1976 Playboy interview—because this is the kind of adultery to which most of us fall victim most of the time. And we don’t even have to be married to commit this kind of adultery. In my view, this is in keeping with the spirit of Jesus’ words about the commandment in the Sermon on the Mount.
But do you see a possible danger with focusing on sin in our hearts? It can start to seem as if sin is an intangible thing that only happens in our heart (or mind or soul). And before long, we imagine that what we do with our bodies doesn’t really matter to God.
Many of us Christians have internalized this false kind of “heart/body” dualism. Maybe this explains why we often take such a casual attitude toward sex. For example, we might think, “We can’t sin by merely having sex with someone to whom we’re not married. Whether it’s sin or not depends on the condition of our hearts.”
If so, we are deceiving ourselves. Jesus’ focus in the Sermon on the Mount on the state of our hearts should not be construed to mean that the external action doesn’t matter. Besides, how can we—self-justifying sinners that we are—begin to judge the purity or quality or motives of our hearts in the first place?
We can safely assume that if we’re justifying our actions in these terms, our heart is wrong, too.