Thanks for the question. The use of the word again corresponds to Jesus' use of the word in John 17:18:
|18 I lay down my life that I may take it again . . . and I have power to lay it down: and I have power to take it up again.
This notion of again speaks to the return to a living state from an apparently dead state.
If I were to say, I will live again, you would conclude that after my death I will return to the former state of aliveness. Of course, as Christians we understand that this return is actually an improvement into a glorified state, which is the fullness of what God intended for us.
So, this application to the Resurrection is simply emphasizing the point that death is no more; life has returned. This is both a body and soul reality.
With respect to the phrase you quoted, come to judge the living and the dead, this speaks to the public judgment that will occur at the Second Coming. All souls experience a Private Judgment after death, but there is a public dimension, which will completely demonstrate the justice of God.
Think of it like secret files that are finally declassified.
- You want to know why satan is damned for all eternity, or all the other demons, or all the souls who didn't make it?
You will see from God's perspective, His Perfect Justice. Likewise, the just will be vindicated in the sight of all. All our sins will be atoned for and will be washed away, and those who are the faithful will be pure as snow. He intends to demonstrate His Justice by revealing His Great Might and Power to transform His children into pure, stainless souls, and likewise our bodies will be given to us in a like manner.
So in context, these phrases disclose a deeper sense of the Christian understanding of judgment and the Resurrection.