"It's a marriage made in heaven." We sometimes hear that at weddings. Sometimes the people who say it don't know just how right they are. Any good marriage has the involvement of heaven, because both parties include God in their marriage.
Some Hebrew scholars have pointed this out in a unique way. They look at the Hebrew words for man and woman and come up with a surprising observation. The Hebrew word for man is "aish" (
, aleph-yod-shin). The Hebrew word for woman is similar. It is "ishah" (
, aleph-shin-heh). The scholars noted that each word differs by one letter. The two different letters, 
(yod-heh, reading right to left), spell one of the names of God, Yah, which is the ending syllable in such names as Isaiah, Jeremiah, and Obadiah. From this they concluded that marriage, the union of man and woman, should include God. They further noted that when you take out the differing letters, both words become a different word, "ash" (
, shin-aleph). This is the Hebrew word that is translated "fire." The conclusion, then, is that a marriage without God is a consuming fire.
Perhaps this gives us a new perspective on the wisdom of the Proverbs. In both Prov 21:9 and 25:24 the writer says, "Better to dwell in the corner of the housetop, than with a brawling woman and in a wide house." In the context of the earlier observation about marriage, and applying the proverb to either a man or a woman, we could rephrase the proverb. Better to live in a corner of the attic with God than to be burned in the rest of the house with an unbelieving mate. This then becomes a warning against even entering a marriage without ensuring that both parties first live with God.
The Israelites were allowed to marry outside of the nation. Ruth the Moabitess was married to two Israelite men (the second after she was widowed). But there were certain people they could not marry. These were "the Hittites, and the Girgashites, and the Amorites, and the Canaanites, and the Perizzites, and the Hivites, and the Jebusites," (Deut 7:1, 3) the seven nations they were to drive out of Canaan. The reason they were not to marry from these nations was that wives from them would not give up their gods and "they will turn away thy son from following me, that they may serve other gods" (Deut 7:4). God had given these people 400 years to learn of Him, and yet they had refused. They were not about to change, and so a marriage with one of their women would end up consumed by fire.
Marriage is an honorable thing, created from the beginning. Marriage is designed to last for a lifetime. Imagine a Jew spending a lifetime trying not to worship the gods of his foreign wife. Imagine a lifetime being "burned" by your mate because you can not agree to give God a place at the dining table or in the bedroom.
There is no law against marrying an unbeliever. There may even be the exception in which a godless marriage lasts through the sheer doggedness of the mates. On the other hand, some surveys say that the two things that cause the most problems in marriages, especially after there are children, are money and religion. The marriages may stay together, but there is often a burning fire separating the two. Instead, a union between a man and a woman, an "aish" and an "ishah", that includes Yah will likely avoid the "ash" that comes from burning each other up.