In 2 Samuel 22:2, this signifies the defense which divine good provides through divine truth. (Apocalypse Explained 316[10])

In Jeremiah 48:18, this signifies defense against falsities and evils from the literal sense of the Word. (Apocalypse Explained 727[4])

In general, a fortress, or bulwark, relates to divine good.

(Odkazy: Apocalypse Explained 316)