So, let’s just start by agreeing that this page is far too small to contain comprehensive teachings on every subject for the topic of separation, but we are able to hit upon a few important teachings. This topic is as important today as ever, but not just for the reasons you might think.
First of all, the most important thing to remember is that in the eyes of Christ, who is ready to judge the living and the dead, the separation is as great a divide as there is between those who are alive and those who are dead. We see in Matthew 13:30 - Let both grow together until the harvest: and in the time of harvest I will say to the reapers, Gather ye together first the tares, and bind them in bundles to burn them: but gather the wheat into my barn. In another place we are told “before him shall be gathered all nations: and he shall separate them one from another, as a shepherd divideth his sheep from the goats:” in the eyes of Christ, things are pretty well separated, and we can never work in ourselves the separation that He is looking to see when He judges. That only comes from Him by responding in Faith to the gospel of Christ as the Holy Spirit persuades us of sin, righteousness, and judgment to come.
For the believer, we are called to live out in truth what Christ has done for us in fact, which is that He has separated us unto God, by His own blood. since God has separated us unto Himself by the blood of Jesus Christ and the working of the Holy Spirit, we are called to follow Him, and by virtue of that following the separation of a child of God from the world is a very natural process. I say that because of the new nature we are given, not according to the old nature that is crucified with Christ which can never please God.
Our separation comes in several aspects. Our eternal destinies are separate from the children of disobedience who have not believed the gospel (2 Thessalonians 1:8). Our manner of life is separate in the way that our appetite for the things of God overcomes the old appetites of the flesh (1 Peter 4:4). The praise we seek is separate from the praise that those who live for the world seek (John 5:44). The only glory we know and speak of is what belongs to Christ for what He has done for us (Galatians 6:14). Our righteousness is separate from the righteousness that others seek (Philippians 3:9).
Having been regenerated by the Spirit of God by faith in Christ Jesus, we are now no longer servants of sin, enemies of God, or children of wrath, but have been separated unto God as a chosen generation, a royal priesthood, an holy nation, a peculiar people; that ye should shew forth the praises of him who hath called you out of darkness into his marvellous light. (1 Peter 2:9) Walk worthy!