In my post, Fornication: What Does It Mean? Part 1, I used sources to prove that in both the English and the Greek fornication includes sexual intercourse by a married person with someone other than his/her spouse. The objection raised by those that hold to a no divorce and remarriage view is that when both adultery and fornication are used in the same text, fornication cannot refer to a sexual act committed by a married person.
In other words, if the word adultery is also used in the text (Matt 19:9), then fornication cannot also refer to adultery. They argue that both words cannot be used in the same text to refer to the same act. This is the point that I want to focus on in this post, and I am going to demonstrate that argument to be false by the scripture.
"Notwithstanding I have a few things against thee, because thou sufferest that woman Jezebel, which calleth herself a prophetess, to teach and to seduce my servants to commit fornication, and to eat things sacrificed unto idols.21 And I gave her space to repent of her fornication; and she repented not. 22 Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds." Revelation 2:20-22 KJV
In verse 20 John says that Jezebel seduced God's servants to commit "fornication;" yet, in verse 22 it is said that they committed "adultery" with her. Here is a case where both "fornication" and "adultery" are used in the same text and refers to the same act. This verse alone proves their argument wrong.
The same point can be made about Israel, God's wife, in the Old Testament. The reason that God put Israel His married wife (Jer 3:14) away was adultery (Jer 3:8); however, when she went after other nations God called it fornication (Ex 16:26 & 29), and said it was as a wife that commits adultery (Eze 16:32) and breaks wedlock (Eze 16:38). I must also point out that God is married to Israel at this point because she had borne him children (Eze 16:20).
The point is, what Israel did with the cities and nations about her was fornication, but the same act was adultery against God. Is was fornication with the nations because she was not in covenant with, but it was adultery against God because she was in covenant (married to, not espoused to) with God.
Apply this same logic to Matt 19:9 and you will understand why both "fornication" and "adultery" are used in the same verse. It is abundantly clear that Matthew 19:9 is referring to the married wife when you read the flow of the text. The wife of Matthew 19:9 is the same wife of Matthew 19:5-6, which all agree is the married wife.