To be understood in the context of shepherd, "rule" is actually "to lead or feed," in the sense of using His shepherd's rod to compel the "sheep" to travel the paths of righteousness (Psalm 23:3,4). On His "rod of iron," see Psalm 2:9.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8