In Genesis God rested on the seventh day after creating everything. In Psalm 95:7-11 God warns Israel to not harden their hearts, otherwise they won’t enter His rest. In Hebrews 3:7–11 that Scripture is used again warning Christians to keep themselves from falling away and becoming hardened by the deceitfulness of sin, vs.12, 13, because, if we do become hardened, we won’t enter God’s rest.
Hebrews 4:3–9 begins with, ‘For we who have believed enter that rest, just as He said, “As I swore in My wrath, they shall not enter My rest,” although His works were finished from the foundation of the world.For He has thus said somewhere concerning the seventh day, “And God rested on the seventh day from all His works”; and again in this passage, “They shall not enter My rest.” Since therefore it remains for some to enter it, and those who formerly had good news preached to them failed to enter because of disobedience, He again fixes a certain day, “Today,” saying through David after so long a time just as has been said before, “Today if you hear His voice, do not harden your hearts.” For if Joshua had given them rest, He would not have spoken of another day after that. There remains therefore a Sabbath rest for the people of God. For the one who has entered His rest has himself also rested from his works, as God did from His. Let us therefore be diligent to enter that rest, lest anyone fall through following the same example of disobedience.’
So the Sabbath corresponds with entering God’s rest in the new covenant. And it is not when we die; it is Today; as verse 3 says, ‘For we who have believed enter that rest…’ In other words, we are saved by grace through faith in Jesus, and not of works. We celebrate the Sabbath by trusting in Jesus. For this reason Paul said to the Colossians, “Therefore let no one act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day —- things which are a mere shadow of what is to come; but the substance belongs to Christ,” 2:16, 17.
Jon David Banks, God’s most unworthy servant