Jesus sent His disciples into the world as those who were different from the world. We don’t have city walls that separate us from others (as in Nehemiah’s day), but we are set apart. Our primary identity isn’t based on our city but on our sanctification.
I do not ask that you take them out of the world, but that you keep them from the evil one. They are not of the world, just as I am not of the world. Sanctify them in the truth; your word is truth. As you sent me into the world, so I have sent them into the world. And for their sake I consecrate myself, that they also may be sanctified in truth. (John 17:15–19 ESV)
This part of Jesus’ prayer is for the Eleven, but has application for all who believe in Jesus’ through their word (verse 20).
For our sake Jesus “consecrated” (ESV) Himself, but it’s the same word used twice. Both could be “consecrated” or “sanctified” (KJV, NASB) or “set apart” (NET).
The point is, the righteousness of Jesus’ every choice, up to His voluntary death as a holy sacrifice, was so that He and we would be set apart. He sacrificed Himself so “that He might sanctify” us (Ephesians 5:26). He died so “that those who live might no longer live for themselves but for Him who for their sake died and was raised” (2 Corinthians 5:15).
So by His life and death and resurrection He is giving us identity as His, security in Him, and making us a community of the consecrated. That differentiates us more than city walls, and He keeps building us up week by week around His Table.