Hebrews 3:7 to Hebrews 4:13. With this warning the comparison between Christ and Moses changes into an exhortation, based on Psalms 95:7-11. This psalm is concerned with the house or community of which Moses was the head, and its lessons are applied to the house of the new covenant. The ancient people of God missed their destiny because of unbelief, and Christians must be on their guard against a like danger. After making his quotation the writer proceeds to explain it by his customary method of allegory. First of all (Hebrews 3:12-19) he points to the solemn warning which is impressed on us by the apostasy of ancient Israel. The danger of unbelief is always present, and Christians must never weary of kindling one another to greater faith; for unbelief is an insidious sin, and grows upon us before we know (Hebrews 3:12 f.). The psalm speaks of an opportunity which is offered to us to-day, and to the writer of the epistle this word has a special significance. It is meant to be prophetic of that interval of time which is still left before Christ returns in glory. The readers are exhorted to make good use of this interval, which is quickly passing. If they can preserve for this little time the faith with which they entered on the Christian life, they will be assured of their place among Christ's people (Hebrews 3:14 f.). The psalm suggests the further reflection (Hebrews 3:16-19) that none can presume to reckon themselves quite secure from the danger of falling away from God. Those who rebelled in the wilderness were no other than the chosen people, who had experienced the great deliverance. They all fell into sin, and were doomed to wander in the wilderness for forty years, until their whole generation perished. God had purposed that they should enter into His rest, but in the end His purpose was frustrated. And it was they themselves who forfeited the promised rest by their disobedience.
It has been conjectured from the insistence on forty years (Hebrews 3:9; Hebrews 3:16) that the writer connected this period in a special manner with his thought of to-day. The interval that would elapse between Christ's death and His second coming was to correspond with that period of forty years which Israel had spent in the wilderness. There would thus be a peculiar urgency in his warning, since the interval of forty years must have been nearing its close before the earliest date that can be assigned to the epistle. But the conjecture, though a possible, is not a very probable one. If the writer had wished to impress on his readers that they could reckon the time of Christ's coming by the OT analogy, he would have taken some means to make his thought more definite.