King James Version
18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
In the eighties I was sitting in one of the most brilliantly alive churches I've ever experienced, where we ran for the front seats in every service, because no one wanted to miss what happened next. The pastor was preaching on this verse, and I suddenly heard from within, "Gates don't move." I fell out of my seat laughing. The thought changed me completely.
For some reason and since I started reading the Bible, I had envisioned a church under attack, and satan's flying attack gates coming at her, but not prevailing. When I heard gates don't move, I knew...the church has to take it to the gates and take them down.
What do gates do, you asked? In times of peace, this whole thread has interesting responses. But gates don't "prevail" in times of peace. They stand opened.
Gates have two purposes: to keep enemies out and to keep captives in. The church destroys the gates of hell and sets captives free. Whom the son sets free is truly free...as free as they once were truly captive.