The one who conquers and who keeps my works until the end, to him I will give authority over the nations, and he will rule them with a rod of iron, as when earthen pots are broken in pieces, even as I myself have received authority from my Father. (Revelation 2:26-27 ESV)
She gave birth to a male child, one who is to rule all the nations with a rod of iron, but her child was caught up to God and to his throne, (Revelation 12:5 ESV)
"From his mouth comes a sharp sword with which to strike down the nations, and he will rule them with a rod of iron. He will tread the winepress of the fury of the wrath of God the Almighty." (Revelation 19:15 ESV)These verses allude to Psalm 2:7-9. In the second Psalm, the Messiah is given the nations as a heritage, and he will break them to pieces because they plot against him. The Psalm says, "I will tell of the decree: The LORD said to me, 'You are my Son; today I have begotten you. Ask of me, and I will make the nations your heritage, and the ends of the earth your possession. You shall break them with a rod of iron and dash them in pieces like a potter's vessel.'" What is of special interest in Revelation (like the LXX) is that the verb "to break" in verse nine is translated as "to shepherd" (ποιμαίνω). The symbol of the Messiah's rod stands for his authority and power to subdue the nations in order to protect and defend God's people.
Revelation uses the symbol similarly; the rod of iron is a symbol of Christ's power and authority. As a symbol, it reveals that Christ uses his power and authority to protect the saints from their enemies and to subdue the unbelieving nations (cf. Psalm 110:5-6). Furthermore, he will share that authority with those who conquer and keep his works to the end.