The first thing that should be acknowledged about South Carolina Governor Mark Sanford's admission to an extramarital affair is that it could happen to any of us. That is not an excuse (and no, it has not happened to me, or to my wife). Every married person has heard the voice; the one that says you deserve something "better."
Gov. Sanford should have been familiar with the voice because of the Bible studies he attended. The voice began seducing humanity a long time ago. It told our first parents that they needed more than the perfection of Eden. The voice told them that God knew that if they ate of the tree of knowledge of good and evil they would be like God. But they already were like God, because they were made in His image.
Stick with me you secularists and non-literalists, because there is a point to be made for you, too.
Psychiatrists explain that married people tire of one another after 10 or 20 years (it used to be seven years, as in that Marilyn Monroe/Tom Ewell film "The Seven Year Itch." Must be inflation.). Good marriages are the result of hard work. Forsaking all others is more than a wedding promise. It is a daily denial of one's lower instincts. Temptation is everywhere. The key to overcoming it is to realize you are fighting an adversarial force that wants to destroy you, embarrass you and cause ridicule to be heaped on the God you claim to worship.
One can make excuses about power and loneliness and starting out as a friendship that develops into something else, as Gov. Sanford rambled on about, but one can't explain adultery. It is what it is and the person who commits it should be calling on God for mercy, not the voters for understanding.
I once asked evangelist Billy Graham if he experienced temptations of the flesh when he was young. He said, "of course." How did he deal with them? With passion he responded, "I asked God to strike me dead before He ever allowed me to dishonor Him in that way." That is the kind of seriousness one needs to overcome the temptations of a corrupt culture in which shameful behavior is too often paraded in the streets.