The "sabbatismos" that remains for the people of God has nothing to do with a day of the week. The Hebrews 4:9-10 passage has to be grossly wrenched out of its wider context to say that. Yes, we are obligated to keep the Sabbath, but that Sabbath we are to keep has nothing to do with a day of the week, but on the contrary has everything to do with resting and remaining in Christ alone by grace alone through faith alone.
It is my observation that churches that maintain a Puritan view of the Christian Sabbath as the observation of a specific day of the week, inevitably without exception end up being legalistic in other areas as well.
~ The Billy Goat ~