I. That it is strongly fortified against those that are bad (v. 1): We have a strong city. It is a city incorporated by the charter of the everlasting covenant, fitted for the reception of all that are made free by that charter, for their employment and entertainment; it is a strong city, as Jerusalem was, while it was a city compact together, and had God himself a wall of fire round about it, so strong that none would have believed that an enemy could ever enter into the gates of Jerusalem, Lam. iv. 12. The church is a strong city, for it has walls and bulwarks, or counterscarps, and those of God's own appointing; for he has, in his promise, appointed salvation itself to be its defence. Those that are designed for salvation will find that to be their protection, 1 Pet. i. 4.