I think the concept derives from Exodus 21:10-11
"10 If he takes another wife, he shall not diminish her food, her clothing, and her marriage rights. 11 And if he does not do these three for her, then she shall go out free, without paying money."
-NKJV
We see that in both instances the man is taking an additional woman while unjustly depriving the other of what is rightfully hers. It seems to be an "if-and" combination. The two scenarios are contrasted in the Exodus passage: on the one hand is a scenario where he takes the additional woman but continues to provide for the other as he is commanded. The other one is highlighted as wrong here and in the Matthew passage... rightly calling out a man's unfaithfulness as it is his covenant obligation to render these to her. He cannot simply rob her of these things and pass them on to the latest hot thing to walk across his path. It is her due.
Thus, if he does the one AND the other, it constitutes a problem. We see many "if-and" promises and conditional statements in the text. Why should this one be treated any differently besides personal bias?
"10 If he takes another wife, he shall not diminish her food, her clothing, and her marriage rights. 11 And if he does not do these three for her, then she shall go out free, without paying money."
-NKJV
We see that in both instances the man is taking an additional woman while unjustly depriving the other of what is rightfully hers. It seems to be an "if-and" combination. The two scenarios are contrasted in the Exodus passage: on the one hand is a scenario where he takes the additional woman but continues to provide for the other as he is commanded. The other one is highlighted as wrong here and in the Matthew passage... rightly calling out a man's unfaithfulness as it is his covenant obligation to render these to her. He cannot simply rob her of these things and pass them on to the latest hot thing to walk across his path. It is her due.
Thus, if he does the one AND the other, it constitutes a problem. We see many "if-and" promises and conditional statements in the text. Why should this one be treated any differently besides personal bias?