Letter 7046: The establishment of divine law provided the beginning of human law, since the commandments found in the Two Tablets...

46. FORMULA BY WHICH MARRIAGE TO A FIRST COUSIN MAY BE MADE LAWFUL. [1] The institution of divine laws furnished the origin of human law, since in those chapters there is read the precept which is shown to be inscribed upon the two tablets [of Moses]. For holy Moses, formed by divine instruction, among other things determined for the people of Israel that they should keep their unions apart from the nearness of pious blood, lest, by returning into kinship, they should both pollute themselves and fail to have a provident expansion into a foreign stock. Prudent men, following this example, transmitted to their descendants a chaste observance reaching much farther, reserving to the prince alone the benefit of joining first cousins in nuptial union, understanding that what they had ordered to be sought from the prince could more rarely be presumed. [2] We marvel at this device, and with astonished consideration we praise the moderation of these matters, that this was left to the judgment of the prince, so that he who governed the customs of the peoples might himself also relax the moderated reins of desire. And therefore, moved by the tenor of your petitions, if only that woman is joined to you by the nearness of a first cousin's blood, and you are proved no nearer to her by any other degree, we decree that she is to be united to you in marriage, and we command that thereafter no question be raised against you, since both our laws consent to this being permitted by our will, and the benefits of the present authority have confirmed your wishes. Therefore, with God's favor, you shall have descendants who are solemnly your heirs, a chaste marriage, a glorious union, since whatever is ordered to be done by us must be reckoned not among faults, but among things worthy of praise.

XLVI. FORMULA QUA CONSOBRINAE MATRIMONIUM LEGITIMUM FIAT. [1] Institutio divinarum legum humano iuri ministravit exordium, quando in illis capitibus legitur praeceptum quae duabus tabulis probantur ascripta. sacer enim Moyses divina institutione formatus Israhelitico populo inter alia definivit, ut concubitus suos a vicinitate pii sanguinis abstinerent, ne et se in proximitatem redeundo polluerent et dilatationem providam in genus extraneum non haberent. hoc prudentes viri sequentes exemplum multo longius pudicam observantiam posteris transmiserunt, reservantes principi tantum beneficium in consobrinis nuptiali copulatione iungendis, intellegentes rarius posse praesumi quod a principe iusserant postulari. [2] Ammiramur inventum et temperiem rerum stupenda consideratione laudamus hoc ad principis remissum fuisse iudicium, ut qui populorum mores regebat, ipse et moderata concupiscentiae frena laxaret. et ideo, supplicationum tuarum tenore permoti, si tibi tantum illa consobrini sanguinis vicinitate coniungitur nec alio gradu proximior approbaris, matrimonio tuo decernimus esse sociandam nullamque vobis exinde iubemus fieri quaestionem, quando hoc et leges nostra permitti voluntate consentiunt et vota vestra praesentis auctoritatis beneficia firmaverunt. erunt vobis itaque deo favente posteri sollemniter heredes, castum matrimonium, gloriosa permixtio, quoniam quicquid a nobis fieri praecipitur, necesse est ut non culpis, sed laudibus applicetur.