I'm not married, nor do I have kids, but I've decided when that time comes I will put my wife first.
It seems to me "your children come first" is the traditional expectation of modern, American society, but I think it's wrong. At least in my case, it led to me being very well treated and doted on within a tragic environment of my parents' relationship falling apart.
This NYTimes blog post [1] captures my feelings pretty well.
> I'm not married, nor do I have kids, but I've decided when that time comes I will put my wife first.
You are not prepared for the hormone storm that you'll experience the first time you hold your child.
For me, I wasn't sure I was ready. I said yes to having kids because my wife wanted kids. The moment I held my son for the first time, on the other hand, all my priorities shifted instantly.
Maybe you'll still hold on to the idea of putting your wife first, but you're not in any position to make decisions about it at this stage and expect them to hold firm.
Actually, now is the perfect time to rationally come up with some sound principles before the hormone storm hits. Hormones are not a good basis for decisions that affect the course of peoples' lives.
Except when the hormone storm hits, you will rationalize to yourself exactly why you need to reverse those decisions with the greatest ease, if that's what fits best.
Hormones control a substantial part of your life, no matter whether you like it or not, and they influence and control a large part of the decision you think you made rationally.
Hormones are the primary basis for most major life decisions. We are animals, not machines. They're not "good" if followed in isolation to memory or reason. But neither is reason good in isolation.
If it wasn't in your best interest as a child for them to act as they did, their mistake was not to put your interests first but to poorly and naively do so, probably by sacrificing the long term to serve the short term. This is isomorphic to the question of naive selfishness vs. enlightened self-interest.
My parents put each other first and were very clear about it. They knew their kids would move out and have their own life. And they would have only each other at that point. So, while I'm sure my mom would have rationed food to the kids first, in any non-survival situation, she'd side with my dad over me.
In front of the kids, I will support anything my wife says over the kids. Period. That is necessary to avoid having kids try to play one parent against the other. (Any attempt to actually play us against each other ends badly for the kids.)
When my kids are teenagers, perhaps my feelings will shift.
But right now my kids come first in my emotional life. I would die for them. I have compromised work for them. It wasn't even a question. I support my wife, but not as unconditionally as I support my children.
This does not mean that I do everything they want. This does not mean that I try to be their lives. I want them happy and healthy, and I do everything that I think is good for them. This is not the same as being their friends. Nor should it be.
Putting kids first explicitly means, to me at least, showing it to your spouse and to your children that she (your spouse) is second only. It may not be deliberate, may not be conscious, but it will manifest in sooner or later. (How frequently it will, depends on how strong this decision is.)
Children not only need loving parents, i.e. parents who love THEM, but also ones who love each other, a couple a model. It's needed for them to want a family, it's needed so that they don't see having children as an obstacle in the way of their personal happiness.
So sometimes, it's beneficial to put the children second, beneficial from their point of view as well. But in general, I don't think there are too many situations when we have to think about who comes first (unless we marry an asshole :) ).
It's a non-quantifiable scenario, whether kids or wife come first. Who do you love more? Does your wife get more Christmas presents more of your time? Does she get more of your time?
In a divorce, both relationships have failed. The base purpose of marriage is to procreate, not that it is necessary, but on some level we realize that this is truth in Western Civilization.
As you say, love is not quantifiable, and it's not a question of who you love more, but to put a different angle on this... in some senses putting your marriage first is putting your kids first.
Kids want a stable, loving environment, and will learn about adult relationships by observing how their parents treat each other (as well as how they treat them). Being around a strong marriage is pretty much the best gift (as well as time) that you can give kids.
I always thought it was a mistake for my parents not to spend more time together outside of their parental roles, and even when I was a kid I could see these as seeds of later turmoil. So whilst this advice isn't directly for you, I'd advise any parents to make some time to enjoy together, away from their kids (so long as the kids are old enough to be looked after by others). Its not selfish if everyone wins.
If you want to argue base purpose, the base evolutionary purpose of pair bonding (which leads to marriage) is to ensure good child care for ones kids. Evolutionarily, men who participate in serial marriage, having kids with each, are very successful. Even though their relationships are not.
Evolution does not care whether your children are happy and healthy. It cares that you have a bunch of them, and they have children in turn.
I am not very successful evolutionarily. Nor do I strive to be.
The first two are backwards. If you doubt me, think about what happens in a divorce.
Disclaimer, I've been married over 20 years and never divorced. My kids come first. I'm fairly sure that my wife puts our kids first as well.