He that is unjust, let him be unjust still. John has just pictured the grand consummation and the blessed state of the righteous. We learn from verse 15 that they are left without the Holy City and not permitted to enter. This verse gives the reason. The one who was unjust on the earth, retains his character, as do the filthy.
Eternity works no transformations so as to make a new creature of a man.
If our characters are not of the kind that we wish to retain forever we had best seek to effect a change on earth. When we go beyond these are fixed. I am Alpha and Omega. The same affirmation is found in chapter 1 . It means that he is from everlasting to everlasting.