This is now NIV shows the parallelism structure in context:
If only there were **briers and thorns** confronting me!
I would march against them in battle;
I would set them all on fire.
Or else let **them** come to me for refuge;
let them make peace with me,
yes, let them make peace with me.”
Briars and thorns are symbols of the unrighteous enemies of God as described earlier in
Surely wickedness burns like a fire; it consumes briers and thorns, it sets the forest thickets ablaze, so that it rolls upward in a column of smoke.
and in Isaiah 10:17
The Light of Israel will become a fire, their Holy One a flame; in a single day it will burn and consume his thorns and his briers.
Briers and thorns are enemies of God and the Israelites. In Isaiah 27:4,5, the parallelism shows that they will either get destroyed or make peace with God. It is a general warning for the wicked then and now.