Hebrews 3:18–19, “18 And to whom did he swear that they would not enter his rest, but to those who were disobedient? 19 So we see that they were unable to enter because of unbelief.”
The audience of the epistle to the Hebrews found itself in the same position as the first generation that left Israel. Like the Israelites, all had agreed to be in covenant with the Lord. And also like the Israelites, not all those who committed to the covenant really believed. God warned the Israelites to persevere in their faith but most of the first generation did not. Only Caleb and Joshua from the first generation were allowed into the Promised Land. Likewise, it was possible that only a few of the Hebrews being addressed in this epistle would persevere and enter into the promises of Christ.
We too are in the same position. We belong to the visible church and not everyone in the visible church is a believer. Some will fall away and be barred from the promises of Christ.
The most important thing to notice in 3:18–19 is the close connection between disobedience and unbelief. In verse 18 we are told that God barred the disobedient from the Promised Land. Verse 19 tells us that the first generation did not enter the Promised Land because of disobedience. This tells us that disobedience and unbelief are ultimately synonymous. If a person professes to believe in the Lord but lives a life of continual disobedience to Him, that person is in danger of being counted among the reprobate.
That unbelief and disobedience are ultimately synonymous should not surprise us at all. They flow into one another. Unbelief leads a person into disobedience of the Lord’s commands, and disobedience to the Lord’s commands leads a person into unbelief. If someone does not really believe in the Lord, that person will have no desire to obey. If a person does not obey the Lord, that person really does not believe in the Lord or His Law.
The connection that the author to the Hebrews draws here between unbelief and disobedience is also important Christologically. The first generation that left Israel disobeyed Yahweh and thus could not enter Canaan. The audience of Hebrews is in danger of forsaking the promise by abandoning Christ in disobedience. The inference is clear. If an Israelite could abandon Yahweh and forsake the promise, and if a person can abandon Christ and forsake the promise, then it is right to conclude that Christ is Yahweh Himself.
When Jesus says “if you love me you will keep my commandments” (John 14:15), He points out the close connection between belief and obedience. Because Jesus is God, His commandments are found from Genesis 1 all the way to Revelation 22. When you say you love Christ, do you also have love for His commandments?