First lets look at whether God care what day we observe?¨
Isa 56:13&14 “If thou turn away thy foot from the Sabbath, from doing thy pleasure on my holy day; and call the Sabbatha delight, the holy of the LORD, honourable; and shalt honour him, not doing thine own ways, nor finding thine own pleasure, nor speaking thine own words: Then shalt thou delight thyself in the LORD; and I will cause thee to ride upon the high places of the earth, and feed thee with the heritage of Jacob thy father: for the mouth of the LORD hath spoken it.”
– “THE¨ is defined as “an absolute, genuine article¨. The verse doesn’t say “a” Sabbath day – it clearly says “the” Sabbath day; it’s very specific.
Exodus 20:8-11, 31:13-17, “Remember the Sabbath day, to keep it holy. Six days shalt thou labour, and do all thy work: But the seventh day is the Sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates: For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the Sabbath day, and hallowed it.”
– Once God blesses, hallows, and sanctifies something it is that way forever. God doesn’t change (Malachi 3:6) nor does His law (Luke 16:17) nor does His Sabbath, nor does His baptism for that matter.(Ephesians 4:5) This verse also specifies a particular definite day; the seventh day, which we call Saturday. It starts at sundown on Friday and ends at sundown on Saturday according to OT reckoning.
Any time one looks up the Sabbath in the Bible it is always described it as being on the seventh day.(Whenever a description is given, that is.) Never is the first day (Sunday) mentioned in this regard.
God is very specific on things – He leaves little to be open to interpretation. Examples would include the exact measurements He gave Noah for the building of the ark (Gen 6:15), the Ark of the Covenant and the earthly sanctuary (Exodus 25:10 thru 36:21), precisely what to do with the lambwhen Passover was established (Exodus 12:8), etc. Do you think the wall of Jericho would have toppled if the children of Israel would have marched around it only 6 times, or did it take the full 7 before the blessing was received? Did a certain someone have to wash in the Jordan river once, or twice, or the full 7 times before his blessing of healing come? God is concerned with details; He’s a God of precision; and He says what He means. He said “the” seventh day. I think He does care what day we observe.
It matters when Christ makes clear it was His day as Creator, He created the Sabbath.