The nations among whom Israel was called to live were unusually degenerate. They practiced public lewdness. Their immorality had spread diseases among their people. They killed their children by throwing them alive into furnaces of fire in worship to their god Molech. To protect the Israelites from these dangerous practices, God had told them not to intermarry with these peoples….
Though intermarriage might look right and proper to us, it would introduce to the Israelites attitudes and concepts that would ultimately undermine their faith and destroy them and their nation. This is what happened. Though Solomon, David’s own son, was said to be the wisest man who ever lived, he contracted over a thousand marriages with foreign women who brought their gods with them and eventually introduced pagan practices into the worship of Israel. By the time Solomon’s son came to the throne, the nation was so divided it could no longer exist as one but was separated into two. So this was a very wise pledge to make.