Have you ever worked on a project for an extremely long time? Perhaps you feel you have crossed every "T" and dotted every "i". You feel like every base is covered and the job was a thorough one that should stand the onslaught of scrutiny. Then the project is shot holes in so quick that you wonder how the project got off the ground to begin with and your spirit deflates at double the speed.
God knows how you feel. He would not be God if He did not know. God established a major project as done - in the beginning. Then He had prophets prophesy about the full manifestation of this project in the future. Then the project was initiated, ran its course and was finished. During this whole process there were always some naysayers trying to poke holes in God's Project - but they were always unsuccessful. It is one thing to break down yours or my project, but a totally other endeavor to challenge The Lord's Project.
In Hebrews 4, the main thought is trusting in the Finished Work or Project of Christ - our Salvation through His sacrifice. Trusting in Christ's complete work allows for believers to enter God's Rest.
God's rest was established when He rested from His work after the 6th day of creation. We find God's day of rest to be observed on the seventh day of the week, but needed to be practiced every breath we inhale. Even before the act of creation, God, The Great Planner said, "He [Christ] was chosen before the creation of the world, but was revealed in these last times for your sake." (1 Peter 1:20) Our rest in Christ's Redemptive Work was laid out in God's Divine Mind well before its manifestation.
His Rest - that which Christ accomplished for all who believe in His sacrifice - was something the Hebrew people could have entered into through obedience, but they disobeyed and God said, "So I declared on oath in my anger, 'They shall never enter my rest.'" (Psalm 95:11) But God's compassion through Christ is immense. The High Priest of God who is able to empathize with our weaknesses and tempted in every way - did not sin, even at the point of torture, shame and death upon The Cross. That is the definition of Christ's Finished Work.
Now we must rest in His Completed Work or Project. Sure that takes care of our Redemption, but His Work is so mighty that it covers every situation, at any moment in time, of any life in the universe. His Grace keeps on giving and His Salvation keeps on Saving - Rest Assured.