Psalm 19:7 - The Creator’s instructions (law) is perfect - reviving the soul.
Paul: I love God’s law with all my heart (Romans 7:22), and it’s profitable for correction and rebuke (2 Timothy 3:16).
The Father’s instructions tells us a lot about marriage, and sexual immorality. What’s permitted, and what is not. What’s sin, and what’s an abomination.
A man adding wives is permitted (Exodus 21:10), but a wife adding husbands is not permitted (Leviticus 20:10).
We also receive plenty of commentary directly from the Father in regard to his own commandments. Too many believers put the commentary of men above the commentary of the Creator, which is sad.
For example, we read that Leah credits the Creator for blessing her with a new child, because she found her husband an additional wife. This shows it’s righteous to help other sisters in Christ share a godly husband. Which is what Paul wrote in 1 Cor 7:2 (in the Greek), but it’s been swept under the rug in modern translations:
1 Cor 7:2
Nevertheless, to avoid fornication, let every man have his own [heautou – exclusively owned] wife, and let every woman have her own [idios – shared] husband.”
Also, we read in 2 Samuel 12:8 - the Creator tells King David - a man after his own heart - if you wanted more wives I would had given them to you - but why did you sin against me by breaking Leviticus 20:10?
So not only do we see that the Perfect Law of Liberty allows it, but we also have positive commentary from the Father regarding it.
Hebrews 13:8 tells us that God is the same yesterday today and tomorrow.
If you believe in the NT - then you must believe in the righteousness of biblical marriage. Some people can’t accept what the word of God truly says regarding biblical marriage, because they may still have the old wine skins. So the new wine is being rejected. New wine calls for new wine skins - as Jesus said - you must be reborn.
Jesus Christ - Luke 16:17 - It’s easier for heaven and earth to pass than the smallest iota to pass from the law.
That concludes that biblical polygyny will remain righteous in the eyes of God as long as earth is still standing.