One of the most important skills that a Christian can develop is biblical interpretation. Judges is a book that gives us plenty of opportunities to grow our skills in biblical interpretation.
Judges 21 is just one example. Here is the story. In the previous chapter, the Israelites went to war with Benjamin (which itself was one of the twelve tribes of Israel). The Israelites nearly wiped Benjamin out but later realized it was in their best interests for Benjamin to survive. However, the Israelites had sworn that they would not give their women to Benjamin and they needed women to survive.
So this is what the Israelites decided. They attacked the inhabitants of Jabesh-gilead and killed them all except for the virgin girls. These they gave to Benjamin. But the Benjaminites needed more women. The Israelites then counselled the Benjaminites to hide in some vineyards and when the the young women of Shiloh came out, they were to forcibly take them.
What a horrible chapter! What kind of God commands people to kill in order to take young girls or to kidnap them by hiding in a vineyard? This is something that we would expect of ISIS.
We should feel uncomfortable when we read this chapter and then we should go back and read it again. Where in Judges 31 does God command them to do any of these things? It was the Israelites that nearly wiped out Benjamin and the Israelites who came up with the plan to get them wives. Just because something is described in the Bible does not mean it is approved by God.
The reader of this chapter should take it a step farther. What is the overall theme of Judges? The message of Judges is that Israel had gone their own way and that the consequences of such a decision were grievous. There is very little in Judges that is held up to us as a good example. We are supposed to read this book and see that Israel was at its lowest point.
So when you read Judges 21, do not see in this chapter divine sanction for you to kidnap a wife. Read the chapter and the book carefully to understand what the author was really trying to say. This is how you do biblical interpretation.
If you are looking for a better understanding of the Bible, take a look at Genesis to Revelation: A Taste of the Entire Bible.