Who's on the defense here?

The theological messaging couldn’t be more dramatic. Jesus says he will build his church—and the “gates of hell” will not prevail against it. We often think of this phrase as though God’s people are in a posture of having to bravely fend off Satan and his demons. This simply isn’t correct. Gates are defensive structures, not offensive weapons. The kingdom of God is the aggressor. Jesus begins at ground zero in the cosmic geography of both testaments to announce the great reversal. It is the gates of hell that are under assault—and they will not hold up against the church. Hell will one day be Satan’s tomb.—Michael Heiser, The Unseen Realm, 284–85 (emphasis original)