But this was never commanded. The only memorial Christ asked us to keep was communion, to show his death. 'Christian Sabbath" is a name thrown on a replacement day.
Okay, well, we'll just agree to disagree, then. I don't have any problem, though, with you calling it a "replacement day," actually. Yes, the Old Covenant sabbath was replaced, at least in a sense. Please allow me to expand just a bit on what the writer of Hebrews tells us... the greater context of Hebrews 10:25, which I pointed out before:
"In speaking of a new covenant, he makes the first one obsolete. And what is becoming obsolete and growing old is ready to vanish away" (Hebrews 8:13)
"...when Christ appeared as a high priest of the good things that have come, then through the greater and more perfect tent (not made with hands, that is, not of this creation) He entered once for all into the holy places, not by means of the blood of goats and calves but by means of His own blood, thus securing an eternal redemption..." (Hebrews 9:11-12)
"Therefore, brothers, since we have confidence to enter the holy places by the blood of Jesus, by the new and living way that He opened for us through the curtain, that is, through His flesh, and since we have a great priest over the house of God, let us draw near with a true heart in full assurance of faith, with our hearts sprinkled clean from an evil conscience and our bodies washed with pure water. Let us hold fast the confession of our hope without wavering, for He who promised is faithful. And let us consider how to stir up one another to love and good works, not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near." (Hebrews 10:19-25)
Certainly, the fourth Commandment is,
"Remember the Sabbath day, to keep it holy" (Exodus 20:8) Jesus, as I'm sure you know, instituting the Lord's Supper, says,
"This is my body, which is given for you. Do this in remembrance of Me” ...and likewise the cup... "This cup that is poured out for you is the new covenant in my blood" (Luke 22:19-20). So yes, it is a replacement, a new and much better way of remembering that the Lord Himself has given us.
The Sabbath was a memorial of the Creation.
Well, I don't really disagree, but it was God's day of rest after His act of Creation, in which He reflected on all He had made and pronounced "very good." And we do the same thing with regard to temporal things and what we have done over the course of the previous week, but now the New Covenant Sabbath is
a looking forward to the eternal Sabbath that we will certainly have in and with Jesus ~ Who finished His work of redemption on the cross... "It is finished!"... and then rose on the first day of the week, Sunday. This is exactly what the apostles and the early church did, as previously pointed out in Acts 20:7 ~
"On the first day of the week, when we were gathered together to break bread, Paul talked with them, intending to depart on the next day, and he prolonged his speech until midnight." Breaking bread... that's Communion, the Lord's Supper, right? They did it on the first day of the week, Sunday.
Grace and peace to you!