God has set aside the seventh day of each week for us to rest; He calls it the Sabbath, tells us to remember it and not do any work on it. (Ex 20:8-10) To walk with God here we must get the day right: He was very specific about the seventh day. So, which day is that?
The Jews, to whom God originally gave the commandments, have been keeping Sabbath on Saturday since before the time of Christ. Christ and the Apostles, who were also Jewish, kept Sabbath the same way; they’ve never been confused about it. If they had it wrong, Christ wouldn’t have agreed with them on it; but He did. (Jn 7:23)
And if we accept Sunday as the first day of the week, the day Christ rose from the dead, then the day before Sunday, Saturday, must be the seventh day. If Saturday isn’t Sabbath, then Jesus didn’t rise from the dead on Sunday.
Since scripture never mentions God changing the Sabbath, why do so many think it’s Sunday? A quick study reveals long-winded arguments based on two irrelevant facts. On Sunday:  Christ rose from the dead (Mk 16:9), and  the early Christians often met together. (Ac 20:7) It doesn’t take a Ph.D in theology to see this doesn’t imply any change in the Sabbath.
People believe in a Sunday Sabbath because that’s what they’re taught; it’s what the Church has claimed for as long as anyone can remember. It’s in her catechisms and liturgies, woven into the fabric of Christianity for nearly two millennia. We might presume the early Church fathers had a good reason for teaching this. Not so.
It started way back in the 1st century with the Fiscus Judaicus: anyone acting like a Jew had to pay a hefty annual Roman tax. It wasn’t long before the early Church began distancing herself from anything and everything that looked Jewish: the Sabbath and biblical feasts, eating clean, circumcision, it all had to go … or pay the tax. Eventually, she rejected her foundation in Torah and invented an entirely new religion.
Persecution: that’s how the Church lost Sabbath. Now, I can’t say I’d have done any better back then, but from the safety of religious liberty, it’s clear we took a wrong turn. The good news is that now, after all this time, we get to re-discover Sabbath, and what a treasure it is!
God made Sabbath for us (Mk 2:27), and it’s a blessing to be able to keep it. God Himself rested on the first one (Ge 2:2), reminding us of His creative power (Ex 20:11), and I’ve no reason to think He isn’t still keeping it, rhythmically inviting us to rest with Him and in Him every Shabbat, reminding us of the gospel, that He’s our eternal rest. (He 4:10)