Adam's original question was well worded and carefully prepared. I'd like to go back to his central question"
Adam wrote:However, I don't find any clear teaching in the New Testament that we should no longer observe the Sabbath. Jesus corrects misconceptions about the Sabbath, stating that it was created for people and not people for the Sabbath, but he never says that it should no longer be observed. The only references I know that could be used to justify doing away with the Sabbath are Hebrews 4:9-10 and Colossians 2:16.
"So then, there remains a Sabbath rest for the people of God, for whoever has entered God's rest has also rested from his works as God did from his." - Hebrew 4:9-10
"Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath." - Colossians 2:16
I think Adam is recognizing that Sabbath and the Lord's Day are distinct. I suspect we would agree that Sunday is not the Sabbath. His question is about whether we should still observe the Sabbath in addition to the Lord's Day. Did I get that right, Adam?
I don't think New Testament Gentiles were ever told to observe the Sabbath. Acts 15 lists the things that Gentiles are to do, and this is not mentioned there. I don't think the early church's writings say that Gentiles observed the Sabbath. Some of them were pretty scathing toward those who demanded Sabbath worship. Here's the Epistle to Diognetes, around 130 AD:
But as to their scrupulosity concerning meats, and their superstition as respects the Sabbaths, and their boasting about circumcision, and their fancies about fasting and the new moons, which are utterly ridiculous and unworthy of notice—I do not think that you require to learn anything from me. For, to accept some of those things which have been formed by God for the use of men as properly formed, and to reject others as useless and redundant—how can this be lawful? And to speak falsely of God, as if He forbade us to do what is good on the Sabbath-days—how is not this impious? And to glory in the circumcision of the flesh as a proof of election, and as if, on account of it, they were specially beloved by God—how is it not a subject of ridicule? And as to their observing months and days, Galatians 4:10 as if waiting upon the stars and the moon, and their distributing, according to their own tendencies, the appointments of God, and the vicissitudes of the seasons, some for festivities, and others for mourning—who would deem this a part of divine worship, and not much rather a manifestation of folly? I suppose, then, you are sufficiently convinced that the Christians properly abstain from the vanity and error common [to both Jews and Gentiles], and from the busybody spirit and vain boasting of the Jews; but you must not hope to learn the mystery of their peculiar mode of worshipping God from any mortal.
Here's the Epistle of Barnabas:
Further, He says to them, “Your new moons and your Sabbath I cannot endure.” Ye perceive how He speaks: Your present Sabbaths are not acceptable to Me, but that is which I have made, [namely this,] when, giving rest to all things, I shall make a beginning of the eighth day, that is, a beginning of another world. Wherefore, also, we keep the eighth day with joyfulness, the day also on which Jesus rose again from the dead. And when He had manifested Himself, He ascended into the heavens.
There's more like that. I'm not going to try to write a complete essay on this subject.
I see no justification in Scripture or the writings of the earliest church for requiring Gentile Christians to observe the Jewish Sabbath.
The New Testament and the early Church did not "move the Sabbath" from Saturday to Sunday, Sunday is the Lord's Day. Calling Sunday the Sabbath conflates these things. Taking a day for rest and focusing on God and family is wise, and doing that on Sunday makes sense if we celebrate the Lord's Day. But let's not condemn someone who chooses to do this on Saturday instead.
Is it biblical? Is it Christlike? Is it loving? Is it true? How can I find out?