Can you help me understand the meaning of the Sabbath Day in Hebrews 4?

In Hebrews 4, the Hebrew writer is using the analogy of the Sabbath rest
to the future rest for those who enter heaven. To bring this home you
really need to go back to Hebrews 3:12-19. In this section, the writer is
discussing the importance of keeping faithful until the end, otherwise one
can lose his or her salvation. This passage is one of the clearest in
opposition to the very common false doctrine sometimes called “once saved,
always saved.” “We have come to share in Christ if we hold firmly till the
end the confidence we had at first.” The Hebrew writer goes on to use the
historical illustration of the people of Israel. Here he using the example
of the Israelites as they wandered in the desert. In this illustration,
leaving slavery in Egypt is symbolic of us leaving our life of sin as we
are saved. In the same illustration, those who wandered in the desert is
symbolic for us of those who are saved and waiting to enter the promised
land–heaven. The author’s point is that just because we have left our
life of sin (been saved) is no reason to kick back and take it easy. If
through lack of attention we become disobedient, we definitely can be shut
out from the Promised Land–heaven.

Moving to Hebrews 4:1, then, the phrase “the promise of entering his rest”
represents both the promise to the Israelites of entering Canaan; the
Promised Land and the promise to disciples of entering heaven. The point
is that we must make every effort to stay on the path of faith or, like
the Israelites, we will be shut out from the “Sabbath-rest” of God, which
is heaven. We must not be of “those who heard [but] did not combine it
with faith.” The Hebrew writer is making the Sabbath-rest an double
analogy of the Jews in the Promised Land and of us in heaven. Hebrews 4:6
makes this clear. It describes some who have received the gospel but who
fail to enter “that rest” (heaven) because of disobedience.

In summary, if you are one of those who have left your life of sin and
been saved by the blood of Jesus through your repentance and baptism–if
you are now wandering in the desert, ie. learning to rely on God as a
disciple of Jesus, then you must be sure to keep working hard at your
faith so that you will not become spiritually lazy, falling into sin and
therefore never entering God’s promised Sabbath-rest–heaven!

John Oakes, PhD