@tomie @Aldo2 this is another case of the Old Testament being absolutely insane. It is similar to God obliterating Sodom and Gomorrah, including anyone who would look back to it. This scripture was from a time when the Israelites were at war with a nation of people who sacrificed children, and so Moses told people to basically kill everyone so that their nation would be no more, then take all of the "pure" women who still existed there. It isn't as if they would have fended well by themselves, but yeah it still is pretty insane. Even without being said by a prophet, this kind of thing was standard warfare (and kind of still is in some ways, honestly), so it is hard to say how much of it is God commanding this to happen and how much of it is God not intervening in it happening. Does that make sense?

Usually, the way this is explained in Christianity is that these were days before Jesus walked the earth and died for our sins. Since Jesus had not yet died for our sins, people had to face the full brunt of their sins instead. Another instance of this happening is the Great Flood, which killed all but 8 people. It is said that Jesus, after He was killed and before He was resurrected, descended to Hades and taught the Gospel to the people who died during the "days of Noah" so that they might have salvation.

Then there is the concept that the Old Testament may not be something that you should always take completely literally when it comes to matters of how one should act as a Christian. It was written by humans in a different time, and their own morals, fears, and such would have been present in the text. As I said before, it is certainly possible that this is an example of not God's commandment, but God's lack of intervening, as is common especially after Jesus died for our sins. That loops back into the former paragraph as well, as there is no longer a need for God to personally intervene in such large ways as He did in the times of the Old Testament.

It is hard to wrap your head around and even harder to justify, especially by modern standards. It happened thousands of years ago. I understand why it makes people hesitate, as it makes me hesitate as well. What it comes down to for me is that Christians should follow Christ first and foremost, and use things such as the Old Testament as supplementary material mostly second to their own prayers and their own informed judgement. Maybe it's an unpopular opinion, I don't know.

I'm sure there are people who could explain this kind of stuff MUCH better than I could as well. The fact is that I do not have every answer under the sun, I mean I've given two different perspectives here, but I do find it interesting to talk about. Some of it is even perhaps informed by my upbringing, because I was raised Mormon and there is the belief taught that Christians should believe the scriptures as long as they are translated/interpreted correctly. Nobody really knows what "correct" is and our modern minds may not even be able to comprehend it, so that's why I say that prayer and personal meditation should be at the top of the list when considering things like this.