Galatians 4:30 “Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman.”
A very critical principle is established in the verse above that will keep you living the Christian life the way that God intended for you to live it. That principle that is critical to you being who you are supposed to be as a believer is the doctrine of separation. Why would God tell Abraham to cast out his son Ishmael? The reason God didn't want Ishmael and Isaac to live together is because He was establishing that separation is what keeps the promises of God pure. Ishmael was a picture of living in sin; whereas, Isaac was a picture of God’s promise of salvation. Ishmael was a picture of living in the flesh; whereas, Isaac was a picture of living by faith. God wants the believer to understand that separation has nothing to do with you being better than someone else, but it has everything to do with you being who you are supposed to be throughout your entire life.
The doctrine of separation truly does separate believers. Most of the squabbles that are experienced in the religious world have to do with separation. There is a crowd who likes to criticize those who live separated lives from the world and from those who don't believe right. This unseparated crowd wants to make it sound as if those who live a separated life are running people off. My friend, separation doesn't run people off because you can't run people off who were never a part of you. Separation shows the difference between God’s people and the world. God has always wanted there to be a difference between His children and the world, and that is why He established this great doctrine of separation between Ishmael and Isaac. Let me point out a couple of thoughts about the importance of separation.
First, separation isn’t easy or convenient, but it is right and keeps doctrine pure and believers from compromise. You can't run with a crowd that doesn't believe like you without them influencing your doctrine. Two times, Paul asked the believers in Galatia “who” it was that caused them to stray from what they believed. He did not say “what” caused you to stray because it was the “who” in their life that caused them to do the “what” that was wrong. You will never be what you are supposed to be in your Christian walk until you remove the “who” that doesn't believe like you.
Second, you are to separate from the believer who doesn't believe like you. Ishmael and Isaac were half-brothers, but God told Abraham to “cast out” the bondwoman. Yes, you are to separate from the lost world, but you are also to separate from the religious crowd who doesn't believe like you. The religious crowd may be saved, but if they don't believe like you, you are to separate from them.
The critical phrase in the verse above is “cast out.” To cast something away means to throw it away. Never join up with anything that would cause you to be what you are not supposed to be. Reading books from those who don't believe like you and joining those who don't believe like you for a common cause will cause them to influence you for bad. The best thing you can do is cast out of your life any influence, including their religious programming, books, or any material that does not believe like you. Separation is God’s safeguard to keeping you from being influenced by the wrong crowd.