Those who advocate any day worship or Sunday worship should consider these facts. ( I am not against worshiping God on non sabbath days but I want to affirm that besides worshiping God on all the days we need to rest on His Holy day).
The primary argument for not keeping sabbath is “we are under new covenant”.
The new covenant was ratified by the blood of Jesus at His death.
For this is my blood of the new testament, which is shed for many for the remission of sins. Matthew 26:28
Bible tells us that the disciples of Jesus kept Sabbath after after they entered into the new covenant.
And that day was the preparation, and the sabbath drew on. And the women also, which came with him from Galilee, followed after, and beheld the sepulchre, and how his body was laid. And they returned, and prepared spices and ointments; and rested the sabbath day according to the commandment. Luke 23: 54-56.
Also Sunday, the day of resurrection, cannot be the day of worship for the new covenant. We know that after a covenant is ratified we cannot add anything to the new covenant. Since the new covenant was ratified 2 days prior to the day of resurrection Sunday cannot be added to the new covenant as the day of worship.
Brethren, I speak after the manner of men; Though it be but a man’s covenant, yet if it be confirmed, no man disannulleth, or addeth thereto. Gal 3:15
Another evidence that Sabbath was still part of new covenant.
And when the Jews were gone out of the synagogue, the Gentiles besought that these words might be preached to them the next sabbath. And the next sabbath day came almost the whole city together to hear the word of God. Acts 13:42,44. The day Paul chose to gather ‘gentiles’ to share the gospel was on Sabbath. If Paul didn’t observe sabbath he could have asked them to come the next day or any other day in the week. He would have preferred not to ‘judaize’ the gentiles by gathering them on sabbath to share the gospel.
We should also note that Luke recognized the 7th day as sabbath day though he is gentile he always refer to it as sabbath day rather than calling it as Saturday (in his language).[ If Luke was not observing Sabbath then it would be ironical to see a non observer of sabbath for example a Baptist to refer Saturday as sabbath. He would refer it as Saturday. Only a sabbath keeper would prefer to refer it as sabbath instead of Saturday]
John says that he was in spirit on the Lord’s day. The only day Bible ever recognizes as Lord’s day is Sabbath.
Sabbath will be the sign of creation and a day of rest even in the new heaven and new earth. Isa 66:22,23
We don’t keep sabbath to earn salvation but as obedience. Obedience is not legalism. Jesus says if you love me keep my commandments.