“And I will send a fire on Magog, and on those who dwell securely on the isles/coastlands, and they will know that I am Yahweh.”
We note now an expansion of God's judgments. The lands of those who attacked his people will likewise suffer (compare the vivid picture in Judges 5:28-30). They thought that they were safe because of their massive forces, and awaited the return of the armies with great booty. But instead they will have to recognise the power of Yahweh's judgments. The furthest peoples will be involved. God's judgments are far reaching and total.
The isles and coastlands (the peoples across the seas) have not previously been mentioned. Along with all previously mentioned the whole of Ezekiel's distant world has now been included in the catastrophe.