The above video clip is taken from Jesus and the Jewish Roots of Advent >
Why did St. Joseph plan on divorcing Mary? And you’re talking about Matthew 1 there. Again, you have put your finger father on a hotly debated topic. There's a lot of debate about the motive and the intention of St. Joseph in divorcing Mary. Let me just make a few basic points about what is clear and then what elements are unclear. First of all, in ancient Judaism it was the case that when you were betrothed to a woman you were legally married to her, okay, and so any separation from her would be described as divorce, even if you had not yet lived together or consummated the marriage physically, okay. So everybody’s clear on that. So we need to be clear that Mary and Joseph were betrothed but they had not yet come together, Matthew said, in other words they had not yet lived together nor had they physically consummated the marriage. And yet, they were legally married, so it could be described as what we say divorce, or in Greek separation, it just means the word to separate from her or put her away. So that’s the first point.
Second — that's clear. What’s unclear is exactly what his motivation is in doing so. If you go back to Matthew's quote there at the top of page 3 it says:
...and her husband Joseph, being a just man and unwilling to put her to shame, resolved to send her away quietly. (Matthew 1:19)
So we see two elements here. First, that Joseph is just. That’s one of his reasons for divorcing her, or he was a righteous man. Second was that he was unwilling to expose her to shame. Now these two things are kind of in tesion with one another because it's not clear exactly what Matthew means here. The problem is this. On the one hand, what seems clear is that he doesn't want to expose her to shame, right, so he's going to divorce her privately. Now what shame would attend the divorce? Well it’s unclear. People would talk and speculate about what the reasons were for it. One of them will obviously be what? Infidelity. So it appears that Joseph wants to keep people from saying that Mary was unfaithful, right, or speculating about her in ways that would be negative or that would shame her.
On the other hand, whenever we read the text, many people think what? Joseph thought Mary had committed what? Adultery against him, right, that she had been unfaithful and become pregnant during the betrothal period. Now that's a reasonable deduction and it can't be disproven ultimately. But the problem with it is that when Matthew calls Joseph a righteous man, in a Jewish context he means righteous according to the Law of Moses, right. In other words, he would be a law abiding Jew. And if you go back to the Book of Numbers, and Deuteronomy also, if a man discovers that his wife has committed adultery, what does the law command him to do? Well they’d take her to the judges of Israel to have her judged and if she’s found guilty then she's to be put to death. This is Old Testament here, remember the women caught in adultery, so and so forth, in John 8.
So the problem is with that, we all assume that Joseph’s righteous therefore he’s going to put her away because he thinks she has committed adultery. But if he thinks she has committed adultery, and he’s actually a righteous Jewish man, his duty would be actually to bring her to the judges, let them prosecute her and then have her stoned. So his decision to divorce her quietly can be interpreted, and many of the church father’s interpret it as suggesting, that he’s obviously troubled by the situation but that he doesn't think she actually committed adultery, because if he did he would obliged by the law and have her condemned. So there's a mystery here about what his motivations are.
A possibility, and some suggested this, is that in the Book of Deuteronomy 24 it says that if a man finds any undesirable thing, it is ervat debar, it means like a word of…it’s very hard to translate it..some undesirable thing, then he is justified in putting her away. So it is the case that Joseph may have just been bewildered by the whole situation and not known what to do, and decided to separate from her but to do it privately because he wanted to keep her from shame, right. So this is called the Respect Theory, it’s sometimes called that, that Joseph divorces her and out of respect for her he tries to keep it quiet, but at the same time the Innocence Theory, that he doesn't really believe she's committed adultery. If you want more on that theory and that whole issue I would consult a book that was written by Fr. Filas, a Jesuit back in the 40s & 50s. He was the world expert on St. Joseph, he wrote about an 800 page book on St. Joseph, just on Joseph, and it’s got everything. He’ll take you through those different theories again. And again, this is one of those matters that the church hasn’t definitively taught on, right. So you can’t find, at least to my knowledge I haven’t seen yet, a magisterial teaching that endorses any one of those particular theories that were put out by church fathers or modern scholars.