St. John Paul II

“Adultery ‘in the heart’ is committed not only because man ‘looks’ in this way at a woman who is not his wife, but precisely because he looks at a woman in this way. Even if he looked in this way at the woman who is his wife, he could likewise commit adultery ‘in his heart.’

Pope John Paul II, “Blessed are the Pure of Heart,” §2, October 8, 1980 audience, published by Daughters of St. Paul, 50 St. Paul Ave, Boston, MA 02130, l983.