@JulieB67
Perhaps this might help in regards to what God established the Sabbath for and how we see the apostles keeping just the way Jesus said His house of prayer would be.
God said the Sabbath was a Holy Convocation 
Lev23:3
Jesus said:
Mark 11:17 Then He taught, saying to them, 
“Is it not written, 
‘My house shall be called a house of prayer for all nations’? But you have made it a ‘den of thieves.’ ”
What is Jesus quoting....
Isa 56:1 Thus says the Lord:
“Keep justice, and do righteousness,
For My salvation 
is about to come,
And My righteousness to be revealed.
2
 Blessed is the
 man who does this,
And the son of man 
who lays hold on it;
Who
 keeps from defiling 
the Sabbath,
And keeps his hand from doing any evil.”
6 “Also the sons of the foreigner
Who join themselves to the Lord, to serve Him,
And to love the name of the Lord, to be His servants—
Everyone who keeps from defiling t
he Sabbath,
And holds fast My covenant—
7 Even them I will bring to My holy mountain,
And make them joyful in My house of prayer.
Their burnt offerings and their sacrifices
Will be accepted on My altar;
For My house shall be called a house of prayer for all nations.”
What did Jesus say His people would be doing in His house of prayer?
Everyone who keeps from defiling 
the Sabbath,
And holds fast My covenant
Why we see both Jews and Gentiles in God's house of prayer (assembly) keeping 
every Sabbath decades after the Cross
Acts 13:27 For those who dwell in Jerusalem, and their rulers, because they did not know Him, nor even the voices of the Prophets which are read
 every Sabbath, have fulfilled 
them in condemning 
Him.
Acts 13:42 So when the Jews went out of the synagogue, the Gentiles begged that these words might be preached to them the 
next Sabbath.
Acts 13:44 On the
 next Sabbath almost
 the whole city came together to hear the word of God.
Acts 15:21 For Moses has had throughout many generations those who preach him in every city, being read in the synagogues
 every Sabbath.”
Acts 17:2 Then Paul,
 as his custom was, went in to them, and for three 
Sabbaths reasoned with them from the Scriptures,
Acts 18:4 And he reasoned in the synagogue 
every Sabbath, and persuaded both Jews and Greeks.
And God's house of pray continues in this same assembly on the Sabbath for worship for eternity, thus saith the Lord. God does not change. 
Mal3:6 Heb 13:8
Isa 66:23 “
For as the new heavens and the new earth
Which I will make shall remain before Me,” says the Lord,
“So shall your descendants and your name remain.
23 And it shall come to pass
That from one New Moon to another,
And from one Sabbath to another,
All flesh shall come 
to worship before Me,” says the Lord.
God identified only one holy day for Him, in all of Scripture, sadly man assigned God a day He said was for works and labors that most keep in lieu of what God said to do.
This is God speaking here...
Isa 58:13 “If you turn away your foot from
 the Sabbath,
From doing your pleasure on
 My holy day,
And call 
the Sabbath a delight,
The holy day of the Lord honorable,
And shall honor Him, not doing your own ways,
Nor finding your own pleasure,
Nor speaking 
your own words,
The end times is about worship. Do we worship God the way He tells us to, or follow what's popular by man's traditions.
Lets not be cheated
Col 2:8 Beware 
lest anyone [e]cheat you through philosophy and empty deceit,
 according to the tradition of men, according to the basic principles of the world, 
and not according to Christ.
We are told to get back to worship our Creator 
Rev 14:7 which is what the Sabbath is about 
Exo20:11