Actually a Google search(which sometimes doesn't do a good enough job with something like this)...
"While the Old Testament permitted polygamy in some circumstances, the New Testament and Jesus' teachings strongly emphasize monogamy as the ideal for marriage. The New Covenant, established through Jesus, doesn't explicitly condemn polygamy, but it clearly portrays the ideal of one man and one woman being married for life, and this is the standard upheld by the church."
Here's a more detailed explanation:
Old Testament Context:
"The Old Testament allowed for polygamy in certain situations, such as when a man died without a male heir (requiring his brother to marry his widow) or when rich men had multiple wives. However, it wasn't the norm, and there are examples in the Old Testament of polygamy leading to significant problems and family discord."
Jesus' Teachings:
"Jesus' teachings on marriage strongly point towards monogamy. When asked about divorce, he referred back to the original creation narrative in Genesis, where God created one man and one woman. This suggests that monogamy is God's original design for marriage."
New Testament and the Church:
"While the New Testament doesn't explicitly forbid polygamy, it clearly upholds monogamy as the ideal. A polygamist is ineligible for leadership in the church (1 Timothy 3:2, 12; Titus 1:6)."
The Ideal of Unity:
"The concept of "one flesh" in Genesis, where a man and woman become one, is central to the biblical understanding of marriage and is consistent with the idea of a single, committed relationship."
A Note on God's Will:
"While God may have permitted polygamy in certain circumstances in the Old Testament, it's important to remember that it was not his ideal or preferred way of life. The examples of polygamy in the Old Testament often show the negative consequences of having multiple wives."
https://www.gotquestions.org/polygamy.html
Jesus's death, burial and resurrection was the beginning of restoring mankind back to what was originally intended in the garden before Adam and Eve sinned throwing humanity into compete and utter turmoil(Gen 6:5-7). God's plan for marriage way back then, is part of what Jesus came to restore(II Cor 5:17.. "we are a new creation"; Rev 21:5..."... behold, I am making all things new". How was marriage taught when all was new "In the beginning..."(Gen 2:18-25, all in the singular). Then Jesus referring back to this verse in Matt 19:3-8 saying, "Some Pharisees came to Jesus, testing Him and asking, “Is it lawful for a man to divorce his wife for any reason at all?” And He answered and said, “Have you not read that He who created them from the beginning made them male and female, and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’? So they are no longer two, but one flesh. What therefore God has joined together, let no man separate.” They said to Him, “Why then did Moses command to give her a certificate of divorce and send her away?” He said to them, “Because of your hardness of heart Moses permitted you to divorce your wives; but from the beginning it has not been this way."
Polygamy was allowed during the Old Testament during very harsh times, but Jesus came to restore that which belongs to Him back to new, along with the Holy Spirit who will help discern between truth and deception...
I John 4:1-6 says, "Beloved, do not believe every spirit, but test the spirits to see whether they are from God, because many false prophets have gone out into the world. By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God; and every spirit that does not confess Jesus is not from God; this is the spirit of the antichrist, of which you have heard that it is coming, and now it is already in the world. You are from God, little children, and have overcome them; because greater is He who is in you than he who is in the world. They are from the world; therefore they speak as from the world, and the world listens to them. We are from God; he who knows God listens to us; he who is not from God does not listen to us. By this we know the spirit of truth and the spirit of error."