Hebrews 4:8-11 For if Jesus had given them rest, then would he not afterward have spoken of another day. There remaineth therefore a Sabbath-keeping [σαββατισμός] to the people of God. For he that is entered into his rest, he also hath ceased from his own works, as God did from his. Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
Notice,
(1) this cannot be the 7th day Sabbath, because it is called ANOTHER day;
(2) the obligation to keep the Sabbath remains;
(3) this new day celebrates Christ’s rest from his work of redemption—the 1st/8th day—as formerly it celebrated God’s rest from his work of creation;
(4) we are to labor to enter this day of rest not only outwardly but also from a heart a faith.
This change from the 7th to 1st/8th day is actually prophesied in the OT:
Ezekiel 43:27 And when these days are expired, it shall be, that upon the eighth day, and so forward, the priests shall make your burnt offerings upon the altar, and your peace offerings; and I will accept you, saith the Lord God.
And it is sung of in the Psalms:
Psalm 118:19-24
Open to me the gates of righteousness:
I will go into them, and I will praise the Lord:
this gate of the Lord,
into which the righteous shall enter.
I will praise thee: for thou hast heard me,
and art become my salvation.
The stone which the builders refused is become the head stone of the corner.
This is the Lord’s doing;
it is marvellous in our eyes.
This is the day which the Lord hath made;
we will rejoice and be glad in it.
On which day were the gates of righteousness opened? On which day did God become our salvation? On which day did Christ, who the Jews rejected, become the chief cornerstone? The day he rose from the dead. The first day of the week. The Lord’s Day.