Scripture’s word used for fornication is porneia.“Living in sin” on the other hand, is not the same - it is a later Christian expression, not a biblical technical term. Let’s compare these two different concepts, which often get confused by churches.
In Scripture, porneia refers to sexual conduct that belongs to the category of sexually illicit or transgressive behavior—often associated with prostitution, exploitation, adultery-like violations, incest, pagan practice, or other conduct regarded as outside legitimate sexual order. In Revelation especially, pornoi are placed among the morally corrupt and ultimately excluded “outsiders.”
The phrase “living in sin” as used by some churches, is not really found in the Bible. It ordinarily means something like:
“Two people are in an ongoing sexual relationship while not being married according to the community's accepted definition of marriage.” There are many examples of people, portrayed in the Bible as saintly examples to copy, who were in such relationships. (For example, Abraham & Hagar, Abraham & Keturah, Jacob & Bilhah, Jacob & Zilpah, David & his wives/concubines.) The scriptures do not condemn those relationships at all.
On the other hand, what is fornication, which scripture does indeed condemn? The biblical material such as in Revelation presents it something along the following lines: sexual conduct characterized as illicit/transgressive, frequently appearing alongside prostitution, exploitation, incest, adultery, idolatry, corruption, and other forms of conduct outside the community's legitimate moral order.
(Note: ChatGPT hits back at this uncharacteristically strongly https://chatgpt.com/share/6ac2896b-1fec-83eb-9765-c69b2d14e48d )
