Dear Parviz and Ali
If I can add my own ten cents to this most interesting issue:
I believe the Zoroastrian concept of "progress" is strictly inward-relative.
This means that progress if not progress from a certain Position A towards a certain Position B where Position B is in advance superior or more perfect than Position A. Because Zarathushtra had no Platonic concept of "ideas being superior to matter". To Zarathushtra, matter was all and was sacred.
The Zoroastrian "progress" is instead a changing/altering/expanding progress moving from a smaller but still perfect Position A to a more expanded but equally perfect Position B. Quite like Spinoza's concepts of change in the monist whole (attributes vs the world-as-one).
To get at this, we just have to remove our PLATONIST projections on these concepts. And with Zarathushtra living 1,200 years before Plato, this also makes perfect sense historically.
This also explains why I have advocated that "haurvatat" should not be viewed as merely a goal (implying that something which has not yet reached haurvatat is not yet perfect for what it is). Haurvatat is rather a state of mind which comes and goes, and our goal is to maintain and dwell within haurvatat as often and as long as we possibly can.
And what is haurvatat then? Haurvatat is whenever and wherever things occur in accordance with asha. And ameretat is the foundation against which all things occur, the timeless qualities of existence.
Try and apply these concepts to Zarathushtra's words in The Gathas and you will soon arrive at a rather complete and sensible worldview!