The phrase "raised arm" refers to great power and intensifies the first phrase. AT: "by my very great power" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-doublet]])
The hand is a metonym for the power that the hand exercises, and the word "lands" is a metonym for the people who live in those lands. AT: "I ... am putting the people who live in all these lands under the power of Nebuchadnezzar ... servant" (See: [[rc://en/ta/man/translate/figs-metonymy]])