1 Corinthians 5:1

Immorality is actually notorious among you, and immorality of a kind unknown even among the heathen??hat a man has taken his father's wife.

James 1:6-8

But he must ask with faith, and without any doubt, for the man who doubts is like the billowing sea, driven and blown about by the wind.

2 Peter 2:14

They have eyes for nobody but adulterous women??yes insatiable in sin. They lure unsteadfast souls. Their hearts are trained in greed. They are accursed!

2 Peter 3:16

speaking of it as he does in all his letters. There are some things in them hard to understand, which ignorant, unsteadfast people twist to their own ruin, just as they do the rest of the Scriptures.

Treasury of Scripture Knowledge

Summary

Unstable as water, thou shalt not excel; because thou wentest up to thy father's bed; then defiledst thou it: he went up to my couch.

Bible References

Unstable

James 1:6
But he must ask with faith, and without any doubt, for the man who doubts is like the billowing sea, driven and blown about by the wind.
2 Peter 2:14
They have eyes for nobody but adulterous women??yes insatiable in sin. They lure unsteadfast souls. Their hearts are trained in greed. They are accursed!
2 Peter 3:16
speaking of it as he does in all his letters. There are some things in them hard to understand, which ignorant, unsteadfast people twist to their own ruin, just as they do the rest of the Scriptures.

Because

1 Corinthians 5:1
Immorality is actually notorious among you, and immorality of a kind unknown even among the heathen??hat a man has taken his father's wife.