Shorter Catechism Q. 70. Which is the seventh commandment? A. The seventh commandment is, Thou shalt not commit adultery. Q. 71. What is required in the seventh commandment? A. The seventh commandment requireth the preservation of our own and our neighbor’s chastity, in heart, speech and behavior.
Commentary: The seventh commandment requires that we preserve “our own and our neighbor’s chastity.” “Chastity” refers to being pure or holy in sexual matters. This will involve abstaining from sex by unmarried persons and engaging in regular sex by married persons.
We are to be chaste in heart, which is to say that we are to be sexually pure in our thoughts and desires. It is not wrong, of course, to have sexual thoughts and desires. The Scriptures only condemn illicit ones. As John Murray says: “The line of demarcation between virtue and vice is not a chasm but a razor’s edge. Sex desire is not wrong and Jesus does not say so. To cast any aspersion on sex desire is to impugn the integrity of the Creator and of his creation. Furthermore, it is not wrong to desire to satisfy sex desire and impulse in the way God has ordained. Indeed, sex desire is one of the considerations which induce men and women to marry…What is wrong is the earliest and most rudimentary desire to satisfy the impulse to the sex act outside the estate of matrimony. It is not wrong to desire the sex act with the person who may be contemplated as spouse if and when the estate of matrimony will have been entered upon with him or her.”
Furthermore, we are to be chaste “in speech, and behavior.” We are to be sexually pure in what we say and in what we do. WLC 138 notes that this will entail “watchfulness over the eyes and all the senses; temperance, keeping of chaste company, modesty in apparel; marriage by those that have not the gift of continency; conjugal love, and cohabitation; diligent labour in our callings; shunning all occasions of uncleanness, and resisting temptations thereunto.”