We need to look at several things with respect to the biblical record. The Bible records that these great saints of the Old Testament on many occasions not only had more than one wife but in some cases (including those of David and Solomon) had hundreds of wives or concubines, which would seem to be in flagrant disobedience to the biblical principles of marriage. Polygamy was in fact flagrant disregard of the design for marriage that God set forth in Creation. I think it's clear not only in the Old Testament record itself but in how the New Testament appeals to the Old Testament, saying that marriage was to be monogamous—one wife, one husband. That's the way it was intended for all generations.
If you look carefully at the opening chapters of Genesis, you will see that after Cain kills Abel, Adam and Eve have another son, whose name is Seth. In looking at the genealogy of these two sons of Adam and Eve, we see that the descendants of Seth are characterized by godliness and righteousness. It was out of that line that Methuselah and ultimately Noah came, as well as Enoch, who was taken directly into heaven because he walked with God.
If you look at the line of Cain, it reads like a rogues' gallery, just one rascal after another. One of the chief rascals, whose biographical sketch is included in the early chapters of Genesis, is a fellow by the name of Lamech, who is distinguished for two things. One is the ghastly sword song that he writes and sings in Genesis, which is a celebration of violence. Also he is noted for being the first polygamist. The Bible doesn't say, "He was the first polygamist and this is a bad thing." It just mentions that he was the first polygamist, but it does so in the context of describing the radical expansion of human corruption and of fallenness. The Old Testament implies that polygamy was in defiance of the law of God.
Obviously, God did not call down these Old Testament heroes for their polygamy or punish them for it. He dealt with their extreme fallenness through forbearance. This forbearance ended with the appearance of Christ and the new covenant.