The Forty-first Lord’s Day

41 The Forty-first Lord’s Day 
Exodus 20:14
You shall not commit Adultery.
In this seventh Commandment are handled those duties which belong to begetting and propagating human life. For these are next in place after those belonging to the preservation of life, which were ranked in the sixth Commandment, which takes care for continuing the life of this and that party in particular. But this seventh Commandment takes care for all men in general. By name then, one special impurity and dishonesty alone is forbidden; but by the usual Synecdoche, or comprehensive sort of speech, all others of that kind are to be understood, whether disordered actions like this, or those that tend of their own nature or of the intention of the doer to further such impure acts.
Doctrine 1. Out of conscience towards God, we ought to keep ourselves from all impurity and unchastity.
Reason 1 . Because sins of this kind bring disorder into those things which belong to the propagation of man’s life, and so they tend in some way to the corrupting of mankind.
Reason 2 . Because from such sins, a sort of most inward uncleanness follows in the person or body of man. This is why the Apostle in 1 Corinthians 6:18; 1 Corinthians 6:1 distinguishes this sin from all others, in that others are outside the body, but this is in and against the body itself. Though there are some other sins that seem to be in and against the body, such as drunkenness, surfeit, etc., yet they neither so inwardly arise from the body, nor so directly and primarily affect it, as do these lustful dishonesties.
Reason 3. Because from this kind of uncleanness follows that dishonouring of our own bodies, which is contrary to what is naturally due to them, and to our persons, as appears in 1 Thessalonians 4:4.2
Reason 4 . Because these impurities in a special way withstand inward holiness, as appears both from that passage in Thessalonians, where holiness is conjoined with the honour of the body in opposition to this uncleanness; and from that passage in Corinthians, where our bodies are said to be temples of the Holy Spirit and members of Christ, yet by these faults they become the members of a Harlot.
Use . Of Admonition: that with greater care and conscience, we shun all such uncleanness. This should all the more be called to mind by us, because the depravity of man’s nature most often appears in these kinds of sins — because they are the most common, most prevalent, and keep the strongest dominion over him. They possess the whole man in whom they are found, and that is most deeply, and with a kind of violence and force. Hence it is that in Scripture they are called a burning, because they burn up everything in their way; and little by little they consume the whole man, as fire consumes the thing that it burns. More especially then, we ought to keep ourselves, 1. From that lust which is properly called carnal, so that we are not subject to it, nor obey its affections and dispositions. 2. From all outward conversation by which such lust is cherished and furthered in ourselves, or in others, as are these:
1 1 Corinthians 6:16-18 Or do you not know that he who is joined to a harlot is one body with her? For "the two," He says, "shall become one flesh." But he who is joined to the Lord is one spirit with Him. Flee sexual immorality. Every sin that a man does is outside the body, but he who commits sexual immorality sins against his own body.
2 1 Thessalonians 4:4-5 that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God;
1. Those thoughts which with pleasure and delight are taken up and engaged with unchaste matters.
2. Wanton apparel and behavior, or which favour wantonness, or cherish it. 
3. Filthy and unclean communication, either in common discourses or songs.
4. Unclean company and wanton representations, as are commonly found in stage-plays and interludes, pictures, and rooms hung with such things, etc.
5. All occasions and provocations to lust, such as idleness, drunkenness, surfeiting, etc. 
6. Most of all, the acts themselves of unchasteness in whoredom, adultery, fornication, etc.
Doctrine 2. By virtue of this command, we are bound to study all cleanness of soul and body that belongs to procreation. 
This is commanded in the same words, that the contrary faults are forbidden by, according to the constant use of speech in the Decalogue. 
Reason 1. Because this cleanness is a part of our inward sanctification.
Reason 2 . Because from this part of our sanctification, a special sort of honour arises, 1 Thessalonians 4:4 — while our bodies are not made drudges for fulfilling the base and vile affections of the flesh, but are applied to nobler uses.
Reason 3. Because this purity is necessary, so that we may be fit to worship God as we should. For where carnal impurity prevails and gets dominion, it not only presses down and burdens the mind so that it cannot raise itself up to spiritual thoughts and affections, but it also infects with contagion, and pollutes those very thoughts and endeavors whereby we seek after and breathe for spiritual life.
Use . Of Admonition: that we do not indulge or allow the inclinations of our corrupt natures in these things, nor allow ourselves to be carried away with the evil manners and examples of the vulgar sort who in this kind, are often more beasts than Christians. But let us always be thinking how we may keep ourselves clean from these lusts of the flesh, as well as from other sins. This cleanness is maintained by modesty and temperance. Modesty is kept in this, if neither by words, nor by gestures, nor by any other such way, we uncover as it were, without reverence, what nature tells us should covered and hidden, and if we are ashamed of the uncovering.
1 Temperance or sobriety consists in keeping a moderation or measure in the pleasures of the flesh or body, especially in food and drink. This cleanness or chastity, as to its diversity of manner, is divided into the chastity of single life, and chastity of marriage. For marriage is appointed by God, since the fall, as a means to keep this cleanness or chastity in things that belong to the generation of mankind. Therefore we ought to have a care, 1. That we marry in such cleanness — that is, with such a person, in such a manner, and for such an end — that from a good conscience it may be said that the contract or bargain was made in the Lord, and in fear of him. 2. That it be used and exercised in this cleanness — that is, that neither the end of it may be broken; nor that it be drawn beyond the bounds of modesty and temperance; nor that it be turned in any way from a remedy for sin and lust, into a cover for uncleanness and wantonness.
1 That is, we are modest if we do not do what is immodest, and if we blush if someone else does.