Imagine that you are a mother trying to raise your only daughter, but due to lack of finances right now, you are living in a bad area. Your daughter is about to enter high school, but the school down the road is filled with crime, and she won’t get a good education there. You have been anticipating this, so you have been working extra hours to save up money for registration for a private school, and you have increased your weekly hours so that you can pay the monthly tuition. When you talk to your daughter about entering this school, she is excited because she was realizing the negative effects of the other school. You tell your daughter that you are willing to continue to save so that she can go to this school, and your only request is that she study hard and try her best to do well. Your daughter is quite gifted and can surely exceed if she sets her mind to it.
She loves the school at first. She does all of her homework and makes good friends. But then, she starts to fall away. She doesn’t do her homework or study the way that she used to. In fact, she starts hanging out with the people who go to the other public school down the road, doing things she knows you wouldn't approve of. She knows of the constant sacrifices you are making for her to go to that school (you are still working constant overtime), but this doesn't reflect in her actions. She still wants to attend the private school and take part in your sacrifice, but she wants to hang out and have fun with the kids from the other school, instead of working for what she has.
This is hurtful and painful to the mother making the sacrifice. The daughter may know that sacrifices are being made, but she clearly does not understand the weight of the sacrifices. This is what we do to God every time we choose sin over Him. We understand the sacrifices that He has made for us, and we want to continue to live in the riches of that sacrifice, but we don’t appreciate it or fully understand its weight. It is an insult to God for us to not take complete delight in the sacrifice He made for us. It is an insult for us to say we know Christ and not be blown away by His greatness. We are commanded to take joy in our God. It is an insult not to. How can we know someone so great, so magnificent and worthy, and know that He gave up everything for us, and still manage to take joy in other things before Him. John Piper writes, “Not to see and savor Christ is an insult to the beauty and worth of his character. Preferring anything above Christ is the very essence of sin” (When I Don't Desire God).
Joy is a command. 1 Thessalonians 5:16 “Be joyful always.”