Thou shalt break them, i.e. those people that will not quietly submit to thee, shall be crushed and destroyed by thee. With a rod of iron; with thy mighty power, which they shall never be able to resist.
Related Commentaries of Psalms 2:9
Psalms 2:9
9 Thou shalt break them with a rod of iron; thou shalt dash them in pieces like a potter's vessel.