what does the bible say?

The first account of a polygamist marriage is found in Genesis 4:19 “Then Lamech took for himself two wives:  the name of one was Adah, and the name of the second was Zillah.”

God never approved or sanctioned the practice of polygamy.  He did permit it in the law of Moses – just as He allowed divorce because of the hardness of man’s heart (Matthew 19:8).  

Nevertheless, according to the Bible, the ideal marital state is one husband and one wife who become one flesh in marriage for life.  God gave Adam one wife (Genesis 2:24).  Jesus also said that from the beginning it was God’s will that a man leave his parents and cleave to his wife (not wives) and the two of them would become one flesh (Matthew 19:4-9). New Testament Scripture also reveals that an elder (I Timothy 3:2; Titus 1:6) or deacon (I Timothy 3:12) is to set the right example and have only one wife.