A valid marriage is one where God enters into the marriage. This is what the Bible says happens in a marriage. God enters into it, and it cannot be broken. In a valid marriage, God is the glue in the marriage.
A close family man friend who had been abused by his father as a child left his wife after 27ish years of marriage. It was difficult for children to process why a good man could leave a good woman.
Too many times, people assume that the marriage was valid and one or the other of the couple had to be "at fault." This leaves people being judgmental of the parties in the couple, or the other spouse, or even self-blame. It takes a long time to heal from that blame.
Many believe that the wife (or husband) has to be a "good enough" woman, so the husband doesn't leave. In other words, the wife has to be somehow "good enough." And that, hopefully, the husband is also "good enough" to put up with any way the wife falls short.
Other people think that the most important thing in marriage is that people "just say no" to divorce. That divorce can never be brought up, that it was the people themselves who somehow had to do the right thing and never divorce. Many people take these approaches as they try to make sense of marriage.
However, ALL marriages have trouble, and God is a really BIG GOD and HE is the glue in the marriage. While it is best if people are "good" and "just say no," those things don't actually work unless God is the glue in the marriage. For instance, in some marriages, the people become mentally ill or substance abusing, or affairs, or even abandonment. If GOD has become the glue in the marriage, then God will give the grace to somehow live out the marriage vows, even if that is separation. The people can never remarry. They are married for life. For "what God has joined together, let no man put asunder."
The practical way of this working out is that the vows have to be fully made to begin with. The vows are what makes a valid marriage. The people have to mean the vows, with NO EXCLUSIONS or CONDITIONS, i.e., that the vows are unconditional.
Examples
Incorrect View: The spouses mean the vows SO LONG AS the other spouse does not have an affair or hit their spouse (or something like that). However, those are conditions. Thus, God is not the glue, and even though the marriage seems valid and the spouses seem to be perfect for each other, it may not last because God is not the glue.
Correct View: A lady friend 25 years ago: Her husband left her and 2 kids and attempted a remarriage. He died of a brain tumor 3 years later. We can't know for sure, and things were obviously very messy for the wife and kids, but it seems likely that the original marriage was valid, and it was a case of "in sickness and in health." She didn't remarry until after her husband's death. It was messy, but that is what the vows imply. In sickness and in health, NO MATTER WHAT MIGHT HAPPEN. Till death do us part, NO MATTER WHAT MIGHT HAPPEN.
Correct View: One of the spouses left the family, had an affair, and the in-laws spewed out numerous names. HOWEVER, they had a valid marriage (i.e., valid vows). Thus, God was the glue and the marriage went back together from such a split that appeared impossible. That is how big God is. When He is the glue, then He is bigger than anything life or imperfect people can throw at the marriage. It doesn't mean it is a storybook marriage. But "God is the glue" means everything.
Vows
Our vows are the most important because that is when God enters the marriage -- at the vows, as the couple fully and freely give themselves to the other.
One couple married later in life put everything into each other's names in the parking lot with a notary, so they did their best to have a marriage fully given to each other with no conditions - to make the vows real. Neither spouse has been perfect. Because it is a valid marriage, when things happen, one of the couple prays, "OK, God this is your marriage and you better do something, cause I don't know what to do." And interestingly, God does that, often within a day, when to a human mind it seemed an impasse. God is the glue. We don't have to be "good enough," although obviously we would like to be. It is so refreshing that God is the glue. Not either of the spouses. God is the glue.
Additional Thoughts
Sometimes marriages work out, and people perceive that there is some level of the spouses being "more committed' or something that made the marriage work. People even say those kinds of things. However, often people make valid marriage vows without realizing how others do not. It is the vows that must be done fully. No conditions.
It is so common that there are conditions that a person has without even realizing it. For instance, "I married a good person who will never do xyz, but those other people married someone I'd kick out if they did xyz." That is arguably a condition that prevents God from being the glue in the marriage. Thus, sometimes people are judgmental of others and their marriages, because they think it is dependent on the people in the marriage, rather than the marriage working because God entered in their marriage. If God is in their marriage, and they don't realize God is not in the other person's marriage, then they are rather judgmental about the people whose marriage didn't work out, rather than understanding that it is the vows in the marriage that brought God into the marriage as the glue for the marriage.
One thing that is so common is that some think the Bible says that marriages can end if there is adultery. This is a condition that the people inaccurately had in the back of their minds with the vows. Adultery is NOT a reason for ending the marriage that God put together. That is how big the decision is for a marriage. It is really a big decision and a big commitment. Praise God for Him being the glue!!
Vows do not have to be completely understood, as God does not expect people to be theologians to get married. God wants our best effort in the vows. For our age and circumstance. But the vows cannot be with conditions of any sort, and this is an easy one to misunderstand. For instance, no one wants to be in an abusive or adulterous marriage. However, we can even teach our kids and grandkids this concept of making vows with no conditions by explaining the following: A woman and man validly marry such that God is in the marriage, and then he is called to war, and from the horrors of war, the man drinks and carouses and even beats the children and the wife and she must separate for protection. In a valid marriage, God will be the glue and give her the grace to remain un-re-married, and hopefully to speak well of the children's father. In an invalid marriage, the marriage will likely end. It is too much for us normal humans to handle that horrible situation. We leave and blame the other. That is not what God wants. Blame of self or the other shows that the concept of a valid marriage is not understood.
It is far less judgmental to accept that it is NOT the "other" or "ourselves" that caused the ending of the marriage. Marriage ending or lasting is whether God is in the marriage or not. If He is in the marriage, then expect Him to be the BIG GOD that He is and He will work it out somehow. It might be a permanent separation. Yet it is God. And that is the level of commitment that must be made by each party to make a valid marriage. That there can never be remarriage if it was a valid marriage to begin with.
This Biblical view of Marriage is far less judgmental of the spouses. The apparent reason for the divorce does not matter. It is all in the vows as to whether God was the glue in the marriage. That's why the vows are so important. The vows can be understood to the best of our ability, even by children. Go over the vows with everyone. Line by line. The traditional vows. There are so many ways the vows can be wrongly taken, and it is almost always in the wrong interpretation of the vows. So go over them out loud and slowly, talking about each word/sentence. They are important and were developed long, long ago. The traditional vows are also why marriages survived long ago. The vows were generally understood in the prior cultures. The vows are still important, but need a slow look in today's modern world where the interpretation is different than in the past.