Why would Jesus need to be ruling the Earth with an Iron rod?
Because they don't want to listen to and obey the words of the Lord.
Psalm 2
2 Why do the heathen rage, and the people imagine a vain thing?
[SUP]2 [/SUP]The kings of the earth set themselves, and the rulers take counsel together,
against the Lord, and
against his anointed, saying,
[SUP]3 [/SUP]Let us break their bands asunder, and cast away their cords from us.
[SUP]4 [/SUP]He that sitteth in the heavens shall laugh: the Lord shall have them in derision.
[SUP]5 [/SUP]Then shall he speak unto them in his wrath, and vex them in his sore displeasure.
[SUP]6 [/SUP]Yet have I set
my king upon my holy hill of Zion.
[SUP]7 [/SUP]I will declare the decree: the Lord hath said unto me, Thou art
my Son; this day have I begotten thee.
[SUP]8 [/SUP]Ask of me, and I shall give thee the heathen for thine inheritance, and the uttermost parts of the earth for thy possession.
[SUP]9 [/SUP]Thou shalt break them with
a rod of iron; thou shalt dash them in pieces like a potter's vessel.
[SUP]10 [/SUP]Be wise now therefore, O ye kings:
be instructed, ye judges of the earth.
[SUP]11 [/SUP]
Serve the Lord with fear, and rejoice with trembling.
[SUP]12 [/SUP]Kiss
the Son, lest he be angry, and ye perish from the way, when his wrath is kindled but a little. Blessed are all they that put their trust in him."