Sabbath vs. 1st day of the week
As the 7th day Sabbath belonged to Judaism, so does the first day of the week belong to Christianity. The Sabbath was never changed, but a new day was given, the day of resurrection.
Christ arose from the dead on the first day of the week (John 20:1).
Jesus met with His disciples on two consecutive first days of the week (John 20:19,26).
The Holy Spirit was given on the first day of the week (Acts 2) when the church was first formed and believers were immersed into that new body.
Believers came together to break bread on the 1st day of the week (Acts 20:7).
They were instructed to set aside for the Lord a portion of their earnings on the first day of the week (1 Cor 16:2).
The Sabbath will be kept during the millennium (Ezek 44:24), but it does not belong to the church. Believers do not show intelligence when they speak of the Lord's day (Rev.1:10) or the first day of the week as a Sabbath day. These are two distinct days, belonging to two different dispensations.
The Christian "Sabbath" is something that does not even exist, except for the believer resting in Christ both now and in the future. And that is resting in a divine Person, rather than resting in/on a "day."
Though the believer is not under the Mosaic Law, he should not abuse the Lord's day, and if his heart is right and he is able, he should seek to spend it for Him. He should live for the Lord every day, but should also rejoice in having the first day of the week to spend more exclusively for Him, to learn of Him, to gather in His name, and to serve Him.
As he would not think of making an ordinary meal out of the Lord's Supper, neither should he habitually make the Lord's day into an ordinary day.
adapted from FEH.