During all those years Belial shall be unleashed against Israel, as He spoke by the hand of Isaiah, son of Amoz, ' saying, Terror and the pit and the snare are upon you, inhabitant of the land (Isa. xxiv, 17). Interpreted, these are the three nets of Belial with which Levi son of Jacob said that he catches Israel by setting them up as three kinds of righteousness. The first is riches, the second is fornication [zenut, the word translated in the Greek as porneia], and the third is profanation of the Temple. Whoever escapes the first is caught in the second, and whoever saves himself from the second is caught in the third (Isa. xxiv, 18).
The builders of the wall (Ezek. 13:10) who have followed after ' Precept' - 'Precept' was a spouter of whom it is written, They shall surely spout (Mic. 2:6) - shall be caught in fornication [zenut] twice by taking a second wife while the first is alive, whereas the principle of creation is, Male and female created He them (Gen. 1:27). Also, those who entered the Ark went in two by two.
And concerning the prince it is written, He shall not multiply wives to himself (Deut. 17:17); but David had not read the sealed book of the Law which was in the ark (of the Covenant), for it was not opened in Israel from the death of Eleazar and Joshua, and the elders who worshiped Ashtoreth. It was hidden and (was not) revealed until the coming of Zadok. And the deeds of David rose up, except for the murder of Uriah, and God left them to him.
Moreover, they profane the Temple because they do not observe the distinction (between clean and unclean) in accordance with the Law, but lie with a woman who sees her bloody discharge.
And each man marries the daughter of his brother or sister, whereas Moses said, You shall not approach your mothers sister; she is your mother's near kin (Lev. 18:13). But although the laws against incest are written for men, they also apply to women. When, therefore, a brother's daughter uncovers the nakedness of her father's brother, she is (also his) near kin . . .
Notice first that the arguments made concerning sexual immorality appeal to two texts (Genesis 1, as it is also displayed in the Ark narrative and in the Deuteronomistic law code, and Leviticus 18). The New Testament use of porneia, in texts that give more to reference in their contexts also display an appeal to one or the other, if not both (cf. the decree of the Jerusalem Council that restricts Gentiles from practicing those thing prohibited in Leviticus 17 and 18, as well as Paul's coining of the word arsenokoites from the description of homosexuality in Leviticus 18, as well as his appeal to the creation narrative in Genesis 1-2 (1 Cor 5-6; 1 Tim 1:10). Hence, the NT is using this term in the same way that its STJ environment is using it.
Second to this, note that this refers to the marrying of a relative, not just sex with a relative outside of marriage. Lynn Cohick notes that the expansion of these laws to include uncle/niece pairs may present evidence of a direct critique of the Herodian family which had a large number of incestuous marriages among uncles and nieces (Women in the World of the Earliest Christians, 207). The concept presented is the immoral use of the sexual act that nullifies the legitimacy of the marriage, not the marriage that sanctions the legitimacy of a sexual act. That's an important point, since many evangelicals perceive their sex acts to be sanctioned by the act of marriage. This leads to all sorts of distorted practices within marriage, not to mention the question as to why marriage cannot purify other forms of sex that are unproductive as well.
The Testament of Judah
And now, my children, in what things so ever I command you hearken to your father, and keep all my sayings to perform the ordinances of the Lord, and to obey the command of the Lord God. And walk not after your lusts, nor in the thoughts of your imaginations in the haughtiness of your heart; and glory not in the works of the strength of youth, for this also is evil in the eyes of the Lord. For since I also gloried that in wars the face of no woman of goodly form ever deceived me, and upbraided Reuben my brother concerning Bilhah, the wife of my father, the spirits of jealousy and of fornication [porneia] arrayed themselves within me, until I fell before Bathshua the Canaanite, and Tamar who was espoused to my sons. And I said to my father-in-law, I will counsel with my father, and so will I take thy daughter. And he showed me a boundless store of gold in his daughter’s behalf, for he was a king. And he decked her with gold and pearls, and caused her to pour out wine for us at the feast in womanly beauty. And the wine led my eyes astray, and pleasure blinded my heart; and I loved her, and I fell, and transgressed the commandment of the Lord and the commandment of my fathers, and I took her to wife. And the Lord rewarded me according to the thought of my heart, insomuch that I had no joy in her children.
And now, my children, be not drunk with wine; for wine turneth the mind away from the truth, and kindleth in it the passion of lust, and leadeth the eyes into error. For the spirit of fornication [porneia] hath wine as a minister to give pleasures to the mind; for these two take away the power from a man. For if a man drink wine to drunkenness, he disturbeth his mind with filthy thoughts to fornication, and exciteth his body to carnal union; and if the cause of the desire be present, he worketh the sin, and is not ashamed. Such is wine, my children; for he who is drunken reverenceth no man. For, lo, it made me also to err, so that I was not ashamed of the multitude in the city, because before the eyes of all I turned aside unto Tamar, and I worked a great sin, and I uncovered the covering of the shame of my sons. After that I drank wine I reverenced not the commandment of God, and I took a woman of Canaan to wife.
The term is used in this text to display that porneia can be committed within a marriage to an unbeliever or to a relative. Although Judah is not married to Tamar in the first instance, his reason for describing his sexual act with her as porneia is because he "uncovered the nakedness of his sons" (i.e., committed incest with them, as she was their wife, past and present through his youngest son who still lived and needed to fulfill the levirite duty to her). The deciding factor, therefore, is not whether a male and female are married, but whether their union intends to faithfully bring about a covenant child. In the mind of STJ, both of these unions threaten that goal. They are, therefore, classified as porneia, even though the individuals in the case of the unbelieving spouse, are male and female and are married.
Hence, the porn-root has a language family that has expanded from merely referring to prostitution to refer to any sexual activity, within or outside of marriage, that does not fulfill the goal of the creation mandate to fill up the earth with covenant children, which is the goal of God's creation in the display of His glorious victory over death and chaos.
"Thus the term [i.e., pornos] in the biblical tradition was understood generically of a man (the feminine porne designates the harlot) engaging in forbidden sexual conduct, alone or with others, whether married or unmarried" (Jerome D. Quinn and William C. Wacker, The First and Second Letters to Timothy, 87).
Since the term in STJ and the NT is based upon the logic of what is considered a good sexual act according to the creation mandate in Genesis 1:28, as it is displayed in the examples of sexual acts that would be prohibited by its observation, found in Leviticus 18, the term cannot merely refer to "sex outside of marriage," but instead, any sexual act, in which one purposely engages, that frustrates or hinders the goal of God's creational purposes in that union.