A Levite living in the hill country of Ephraim took a concubine (something like a common-law wife) but she was unfaithful to him.  This unfaithfulness doesn't necessarily mean she committed adultery, but that she simply left him to go back to her father's house.  The Levite went after his concubine and on the way back home with her, stopped at Gibeah.  The common practice of the day when traveling was to go into the city and sit in the city square until someone offered a place to stay for the night.  An old man offered his house.  Wicked men of the city came to the old man's house demanding that he send the man out to them so they could have sex with him.  This story is quite reminiscent of what happened in Sodom with Lot and his family and the angels.  The old man offered his virgin daughters, which the wicked men refused, and the Levite man offered his concubine.  The men did disgraceful things to the concubine and she died.  When the man returned home, he cut up the concubine into 12 parts and sent the pieces into all the areas of Israel.  As a result the Israelites decided to do battle against Benjamin.  However, they did not inquire of the Lord before going into battle.  As a result the Israelites were defeated by the warriors of Benjamin in this battle.  After this defeat, the Israelites wept before the Lord and then they inquired of the Lord.  They were still defeated in battle by the Benjamites.  Lastly, the Israelites wept, fasted, presented sin offerings, and then inquired of the Lord.  They were successful. 
Lessons for us today?
We have to learn obedience, make ourselves right before the Lord by repenting of our sins, inquire of Him concerning our decisions, then we will be successful in "battle".  We do battle each day with the evil forces of wickedness.  Our weapons come from God's Word.

The tribe of Benjamin had turned to homosexuality – a practice that God calls an abomination. God used the Israelites to discipline the Benjamites. He wanted homosexuality purged from Israel.  Yet the people grieved for Benjamin.  They had made an oath that they would not give their daughters in marriage to any man from the tribe of Benjamin.  After making this oath, they grieved for Benjamin because this would cause a gap in the tribes of Israel. So they subverted their oath by finding a "loophole".  They couldn't GIVE their daughters to the Benjamites but they could allow their daughters to be TAKEN. (Judges 21:16-24).  The intent of the vow they took was to deny their daughters in marriage to the Benjamites.  They violated this vow, "loophole" or not. 

One of the most profound statements in the Chronological Bible commentary so far is this one. “Religious apostasy is somewhat understandable in an age of idolatry and pagan practices, so it is not surprising to see the Israelites repeatedly lapse into spiritual unfaithfulness."

It is absolutely amazing how applicable this is to our world today. Many of God’s people continue to “fall away” from sound biblical teaching. This is spiritual unfaithfulness. Paul echoed these same words in his letter to Timothy.

2 Tim 4:3-5
For the time will come when men will not put up with sound doctrine. Instead, to suit their own desires, they will gather around them a great number of teachers to say what their itching ears want to hear. They will turn their ears away from the truth and turn aside to myths.

Why would we want to turn away from God's truth and honor pagan practices instead?  Are we, like the ancient Israelites finding a "loophole" to suit our own desires? 

But what a great encouragement Paul gave to Timothy and to us.

But you (put your name here), keep your head in all situations, endure hardship, do the work of an evangelist, discharge all the duties of your ministry.

Even though there may be spiritual unfaithfulness all around us, we must keep on doing the work that God has called us to do...to be His faithful witnesses!