Rainy, I too agree that the sabbath was never changed to sunday. That would negate the whole point that Jesus fulfilled the sabbath, and now we rest in His works everyday.
Have you ever noticed that on the seventh day of creation, there is no morning and no evening? To me that has significant meaning. That was the day that God rested from His works, yet it never says that ended. This is one of the reasons I say the Sabbath is very important, but I believe the Sabbath now means an eternal rest in Christ, just as it was intended before the fall of man.
This is what I believe Hebrews 4 is talking about, entering the eternal rest in Christ.