“broken” =  luo = to loose any person (or thing) tied or fastened, such as shoes, chains, or bonds. Thus to loose what has been built together; to dissolve, to destroy or do away with.

“the scripture cannot be broken” = Morris makes the observation that Jesus does not make this statement about one of the great declarations of the Old Testament, but about this rather insignificant verse (in relation to some other passages). The point is that all scripture is God-breathed and cannot be done away with, no matter how insignificant we may consider it to be, nor due to how it may conflict with our own doctrines. It retains all of its power even in the face of being supposedly “proven” to be in error.