God’s promise of entering "His rest" still stands, so..... WE (believers) ought to tremble with fear that.... "some of you" might fail to experience it.
FOR..... this good news—that God has prepared this rest—has been announced to us just as it was to them. But it did them no good because THEY.... did not share "the faith" of THOSE "who listened" to God.
FOR..... only "we who believe" can enter..... His rest. As for the others, God said, “In my anger I took an oath:
THEY.... "will never enter My place"... of rest, even though "this rest" (in Christ)  has been ready since He made the world." (Hebrews 4:1-3)

God’s rest is there for (God's) people to enter, but THOSE who first heard this "good news" FAILED to enter because THEY.... disobeyed God.
SO..... God set another time for entering His rest, (for His people) and that time is TODAY. (for those still alive) God announced this through David much later in the words already quoted:
“TODAY when you hear His voice, (while you are still alive) do not harden your hearts.” (Hebrews 4:6,7)

(Refusing to obey God leads to rebellion and hard hearts - you become a rebel and are against God..... Repent TODAY!)

THERE is...... a "special rest" still waiting for "the people of God."
FOR all "who have entered" into "God’s rest" have rested from..... THEIR OWN labors, just as God did after creating the world. (Not about Salvation)
SO...... "let us" do our BEST to enter that rest. (NOW) BUT..... "if we disobey" God, as the people of Israel did....... WE TOO WILL FALL. (Hebrews 4:9-11)