So the angel that communed with me said unto me, Cry thou, saying, Thus saith the LORD of hosts; I am jealous for Jerusalem and for Zion with a great jealousy. And I am very sore displeased with the heathen that are at ease: for I was but a little displeased, and they helped forward the affliction. Therefore thus saith the LORD; I am returned to Jerusalem with mercies: my house shall be built in it, saith the LORD of hosts, and a line shall be stretched forth upon Jerusalem. Cry yet, saying, Thus saith the LORD of hosts; My cities through prosperity shall yet be spread abroad; and the LORD shall yet comfort Zion, and shall yet choose Jerusalem. (Zechariah 1:14-17)
The God we serve is a jealous God, He wants us to serve Him and Him alone. And He has every right to expect us to do so since He has blessed us with the great honor of being created by Him. He is our Creator.
He chose the Hebrews to be His, He chose Jerusalem to be the place where they would worship Him. And as the sight of worship it must be dedicated to Him, it should be exactly as He has desired; clean from immorality and false idols, the unbeliever should be uncomfortable being in the place God has chosen to call His own unless they get right before His eyes. Yet this isn't what was found in Jerusalem. There was no wall, no separation. The cultures had mixed and the Hebrews allowed there to be compromise in their walk. They had made things comfortable for the outside world to come in. God's holy land and His chosen people had become polluted. And so the Lord tells Zechariah He will build a wall.
You see, the Lord wants us to be separate. He always has. He called the Hebrews to walk a different life, to follow a different path, to walk the only path to Him. This path eventually led the way to Jesus (and at this point there were those who refused to continue on the path) and after His death and resurrection the doors were opened to the Gentile. Now we can step onto that path and follow. But, and here is the key, the path Christ has laid out does not lead into the world, but away from it. Christ's death did not open the doors so that the Jews might go out (though some did and still do), but so that the Gentile might come in. He calls us to join together with our brethren and head to Jerusalem, to head to His presence. And He calls us to be separate. When we come to Christ He calls us to step inside the protective walls of the city - of His presence.
Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned. (John 15:4-6)
Notice that phrase, "come to Christ." Have you ever wondered why it is we say that? It is one of those things that I just picked up being around other Christians, I never really stopped to think about what that meant for quite some time. I believe this phrase is used, because it shows the action that must be taken. He calls us to Him. He may meet us where we are, but He calls us to follow Him in righteousness, He calls us to deny ourselves and follow (Matthew 16:24). Follow where? To the Father, of course.