The first olive out of the jar is Christians are forbidden to be unequally yoked (2nd Corinthians 6:14), which is pretty clear in commanding Christians to only marry Christians. For Christians faith is the foundation on which marriage is built. It establishes a common worldview and standard of authority under which the marriage is governed. The various aspects of faith that could or should be part of the lives of the believers is enormous. All this is a structure.
In the long run though, in order for a marriage to flourish something has to be present within that structure that doesn't have anything to do with faith. Meaning, something that is possible regardless of whatever faith a person might ascribe to.
In Genesis 3:16, God said "your desire shall be for your husband and he shall rule over you." What does that mean? [Woman shall desire] the [Man who rules over her]
Ergo, her desire is for a ruler. It's a two-edged sword that says wives will desire their husbands, who shall rule said wives, but implied is the husband must be fit to rule in order to be desirable. That doesn't get taught. If he is not desirable (attractive) to his wife, she will chafe under his rule and there will be problems with rebellion in the kingdom. If he's a Turkey, there could be an attempted coup. (sorry, I had to)
The one common factor I can point to in successful marriages is a husband who is fit to rule, who provides the balance his wife needs. In some areas he is a stern and unmoving oak tree and she can scream, wail and cry with her tears falling like rain, but he is completely unmoved. In other areas he is tender and compassionate. Just like any good ruler who loves his subjects. Likewise, I notice in marriages that are poor or in situations in which the marriage failed, the husband is not or was not a fit ruler. The vast majority of the time, he was all comfort and snuggles but couldn't bring himself to be strong and stern when needed. I get tremendous resistance from men for pointing this out, but it's true.
Athol Kay wrote the book "Married Man Sex Life Primer" and I honestly think if every husband read the book and put what he says in practice, the rate of divorce would plummet. He defines the fitness to rule in terms of alpha and beta with their corresponding hormone responses of dopamine and oxytocin. He does quite a good job of making sense of it and backs up what he says. In addition, all men should read the books by Rollo Tomassi: "The Rational Male" and "The Rational Male: Prescriptive Medicine" before they even consider getting married. Athol is an atheist, formerly a conservative Christian Kiwi. Rollo is a professed Christian although I don't know what that means to him.
One claims to have had faith, one claims to have faith, both of them know what they're talking about. I, of course, have a long history as being a rather disreputable fellow, a known heretic and iconoclast, an admitted adulterer of legendary proportions, a world traveler who has a thick file with multiple intelligence services, an all-round troublemaker and raconteur who was once arrested for the desecration* of a national shrine with a "public display of phallic contempt."
And yet, I am saved by grace, through faith.
So, I am not at all making light of the need for faith or the impact of faith within a relationship, but I do know this: her desire (attraction) is far more important in marital relationships than the vast majority of people of faith are willing to admit. And because of feminism, you will seldom if ever hear a sermon on Genesis 3:16, unless it's to talk about how the curse has been lifted.
As to faith, it is given to man to live, to die and then judgment; and faith will determine whether one stands in the day of judgment before the White Throne, or whether one kneels before the bema seat.
As to marriage, the authority to initiate marriage is the birthright of each individual man. Why a man chooses to marry is up to him and others may think the reason wise or unwise, but it is his to make. Likewise the choice to take more than one wife. There are plenty of people who will say wanting more sex isn't a reason to take another wife or taking another wife should only be done because God called you to do so... and while everyone is free to have an opinion, ultimately it falls to the individual man and what he wants.
A lot of men might want a plural marriage, but the perception of how fit he is to rule will determine how attractive he is, which will determine whether he gets married at all. His actual fitness or lack of fitness will in large part determine the success or failure of any marriage he gets.
*I did apologize and I truly meant no disrespect, it's just that it looked like a canal, Japan doesn't do public toilets and my back teeth were floating. And if there had been even one sign in English saying it was the moat of the Imperial Palace, I wouldn't have pissed in it.