“Your righteousness is an everlasting righteousness.”
The kind of righteousness in the law of Moses came by the proper use of earthly things: fire, stone, and animals for the sacrifices; water, bowls, and special clothing for worship; etc. That kind of righteousness is fleshly; it is not eternal because it is bound to natural things.
God’s kind of righteousness, on the other hand, is spiritual, not fleshly, and it will endure forever. Jesus suffered and died to make that kind of righteousness available to us, and he succeeded! The holy Ghost brings into our hearts God’s kind of righteousness, and that wonderful righteousness will continue in us long after this universe and everything in it has been destroyed.