Jesus and His Apostles Kept the Sabbath

The Old Testament is a shadow and a copy of the New Testament.

Heb. 10:1 『The law is only a shadow of the good things that are coming - not the realities themselves.』

Thus, the law of the Old Testament was a shadow of the good things that were to come in the New Testament times
The Sabbath day in the Old Testament was called "the Sabbath of Jehovah" (Ex. 31:13; Ezek. 20:12), while the Sabbath day in the New Testament was called "the Sabbath of Jesus" (Matt. 12:8; Luke 6:5).
The Sabbath day, according to the Old Testament law, was only a copy.
The Sabbath day of the new covenant, kept in Christ, is the reality.
In the New Testament times, the apostles kept the Sabbath day by worshiping God in spirit and in truth, following Jesus Christ's example.
Jesus kept the Sabbath as His custom.

Luke 4:16 『He went to Nazareth, where he had been brought up, and on the Sabbath day he went into the synagogue, as was his custom....』

In the New Testament times, the Sabbath day is referred to as "Jesus' [the Lord's] day" because the true Lord of the Sabbath is Jesus Christ.
"For the Son of Man is Lord of the Sabbath" (Matt. 12:8; Luke 6:5).
The apostles kept the Sabbath day as the "Lord's [Jesus'] day."

Rev. 1:10 『On the Lord's Day I was in the Spirit...』

As the times of the Old Testament passed away and the New Testament times began, the way in which God's people keep the Sabbath was changed.
However, the day of the Sabbath was never changed.
The day itself could not be changed because it was on the seventh day that God had rested from all of His creating work.
The apostles kept the Sabbath day as their custom, reasoning from the Scriptures as follows:

Acts 17:2 『As his custom was, Paul went into the synagogue, and on three Sabbath days he reasoned with them from the Scriptures...』

Acts 20:6-7 『But we sailed from Philippi after the Feast of Unleavened Bread, and five days later joined the others at Troas, where we stayed seven days. On the first day of the week we came together to break bread...』

As it is written in the above verses, the apostles kept the Sabbath day.
It is proven throughout the Scriptures that the Sabbath day —the seventh day, Saturday, Jesus' day— was kept until the apostolic age.
So why do so many present-day Christians hold services on Sunday [the first day] and not on the Sabbath day?
According to history, Sunday service originated from pagan sun-god worship.
The Romans had been worshiping the sun god on the first day [Sunday], recognizing it as "the day of the sun," even before the birth of Jesus.
Therefore, we have to keep the Sabbath day.
And we should conduct ourselves bearing in mind our duty as God's people.