No matrimony is to be allowed between persons who are not legally eligible.

Since matrimony is a legal union between a man and a woman, great caution ought to be applied lest persons whom the divine laws do not want to be admitted to the fellowship of a union of this kind enter into marriage against legal right and divine law, and are united in its bonds. For if this should happen, incest would contaminate our kingdom and the churches located in it, and these same persons, corrupted by their heinous union, would then of necessity incur the greatest hatred of God.

What consanguinity and relationship by marriage are.

There are many grades of consanguinity and affinity in which marriage cannot take place. But first, in order that these terms may be understood, consanguinity is used to refer to those who were begotten by the same parents by whom we were begotten, or who are descended [from us] through procreation of body and blood. Affinity however, derives from the marriage of male and female. Moreover, these two terms, consanguinity and affinity, have been compared in such a way that first divine laws, and then civil ones, have noted [certain] grades in each category in which marriage should not be entered into in any way.

What kind of divine law prohibits marriage.

God has established a fixed law of these grades in Leviticus 185 and 20; we and all our posterity must be bound by this law. For the precepts of those chapters were not peculiar to the commonwealth of the ancient Israelites (as some imagine), but have the same weight of authority as our religion bestows on the ten commandments, so that no human power can decree anything which is in any way [contrary] to them. Therefore the Roman pope appropriates this power to himself irreligiously, and those who seek dispensations (as they are called) in this matter, either from the Roman pope or from any other person, hurt their own a quocunque alio, tales in hac causa dispensationes (ut vocant) conquirunt. Hoc tamen in illis Levitici capitibus diligenter animadvertendum est, minime ibi omnes non legitimas personas nominatim explicari.