5. Therefore, though the Jewish law cease (yea, never bound other nations) formally as that political national law; yet as it was God's exposition of his own law of nature, it is of use, and consequential obligation to all men, even to this day; for if God once had told but one man, This is the sense of the law of nature, it remaineth true, and all must believe it; and then the law of nature itself, so expounded, will still oblige.
6. The world is so wide for choice, and a necessity of doubtful marriage is so rare, and the trouble so great, that prudence telleth every one that it is their sin, without flat necessity, to marry in a doubtful degree; and therefore it is thus safest, to avoid all degrees that seem to be equal to those named Lev. xviii. and to have the same reason, though they be not named.
7. But because it is not certain that indeed the unnamed cases have the same reason, (while God doth not acquaint us with all the reasons of his law,) therefore when the thing is done, we must not censure others too deeply, nor trouble ourselves too much about those unnamed, doubtful cases. We must avoid them beforehand, because else we shall cast ourselves into doubts and troubles unnecessarily; but when it is past, the case must be considered of as I shall after open.
Quest. II. What if the law of the land forbid more or fewer degrees than Lev. xviii. doth?
Answ. If it forbid fewer, the rest are nevertheless to be avoided as forbidden by God. If it forbid more, the forbidden ones must be avoided in obedience to our rulers.
Quest. III. Is the marriage of cousin-germans, that is, of brothers' children, or sisters' children, or brothers' and sisters' children, unlawful?
Answ. I think not; 1. Because not forbidden by God. 2. Because none of that same rank are forbidden; that is, none that on both sides are two degrees from the root. I refer the reader for my reasons to a Latin Treatise of Charles Butler on this subject, for in those I rest. As all the children of Noah's sons did marry their cousin-germans, (for they could not marry in any remoter degree,) so have others since without reproof, and none are forbidden. 3. But it is safest to do otherwise, because there is choice enough beside, and because many divines being of the contrary opinion, may make it matter of scruple and trouble afterwards, to those that venture upon it without need.
Quest. IV. What would you have those do that have married cousin-germans, and now doubt whether it be lawful so to do?
Answ. I would have them cast away such doubts, or at least conclude that it is now their duty to live peaceably in the state in which they are; and a great sin for them to be separated on such scruples. The reason is, because, if it be not certain that the degree is lawful, at least no man can be sure that it is unlawful. And for husband and wife to break their covenants and part, without a necessary cause, is a great sin; and that which no man can prove to be a sin, is no necessary or lawful cause of a divorce. Marriage duties are certainly commanded to the married, but the marriage of cousin-germans is not certainly forbidden. Therefore if it were a sin to marry so, to them that doubted; or if they are since fallen into doubt whether it was not a sin; yet may they be sure that the continuance of it is a duty, and that all they have to do is to repent of doing a doubtful thing, but not to part, nor to forbear their covenanted duties. No, nor to indulge or suffer those troublesome scruples, which would hinder the cheerful discharge of their duties, and the comfortable serving of God in their relations.
Quest. V. What should those do that are married in those degrees which are not forbidden by name in Lev. xviii. and yet are at the same distance from the root with those that are named, and seem to have the same reason of unlawfulness?