Heb. 3:13. But exhort one another every day, as long as it can be said: "today,"
That is, edify one another and strengthen each other, so as not to fall. And if anyone falls, correct him while he is still alive; this is what the expression means: "while it can be said: 'today,'" for there is hope. And especially, let there not be in anyone an evil heart; but if it happens, let him not fall into despair, but comfort him, and you will win him back again.
Heb. 3:13. lest any of you be hardened through the deceitfulness of sin.
That is, lest from despair he come to hardness and remain incurable. For just as hardened and rough bodies do not yield to the efforts of physicians, so hardened souls do not obey the word of God. By "the deceitfulness of sin" he means either the deception of the devil—that is, not to hope that there will be recompense—or carelessness. For, he says, if I have sinned once, then I no longer have any hope—this is truly the deceitfulness of sin. Sin, deceiving and drawing one to itself, causes one to think in the way that is said: "When the wicked comes, contempt comes also" (Prov. 18:3). And whoever holds in contempt can no longer believe. Thus, from sin comes unbelief. "And they say: 'The Lord shall not see, neither shall the God of Jacob regard it'" (Ps. 94:7). And again: "saying in his heart: 'You will not require it'" (Ps. 10:13), and: "God has forgotten" (Ps. 10:11), and everything of that sort.
Heb. 3:14. For we have become partakers of Christ,
That is, we and He became one, and we became partakers of Him to the same degree that the body is of the head. Here he inspires them with hope, as if saying: He Who loved us so much that He even made us His body will not allow us to be torn away from Him, if only we ourselves do not desire it. At the same time he hints at what is said in another place: "if we endure, we shall also reign with Him" (2 Tim. 2:12). Being now partakers in the same things as Christ, evidently in afflictions, let us strive to be partakers also then in glory.
Heb. 3:14. If only we hold firmly to the life we have begun until the end,
That is, faith; for through it we exist and realize a divine and spiritual existence and regeneration. And here he requires standing firm in the faith until the end.
Heb. 3:15. While it is said: "Today, if you hear His voice, do not harden your hearts, as in the provocation."
He confirms in what sense he said "to the end," and says that this is signified by the expression "today." For "today" means: always, as he also said above: "but exhort one another every day, as long as it is called 'today'" (Heb. 3:13). Or, what is more approved, as stated by Saint John Chrysostom, the apostle makes a transition from the words "as long as it is said: 'today, when you hear His voice,'" to what follows: "Therefore let us fear, lest, while a promise remains" (Heb. 4:1), and so on.
Heb. 3:16. For some, when they had heard, did provoke;
Having heard, he says, God's promise — "I will give you the land of Canaan" — they did not believe, and by their unbelief they provoked God to anger. See to it, then, that you also do not be unbelieving in the promises. For hearing alone will not benefit you if you do not also believe. Just as hearing did not benefit them either, but on the contrary, they perished with complete justice precisely because they did not believe the words of God.
Heb. 3:16. But not all who came out of Egypt with Moses.
Caleb and Joshua the son of Nun were not among the unbelievers, and therefore attained the promise and entered Palestine.
Heb. 3:17. And with whom was He angry for forty years? Was it not with those who sinned, whose bones fell in the wilderness?
He concludes his speech with a question for greater clarity and less contradiction. Questions are posed to those who are confessing. He also proposes the punishment. Their bones fell in the wilderness, he says, that is, the large thighbones. Through a part he indicated the whole bodies.
Heb. 3:18. And to whom did He swear that they would not enter into His rest, if not to those who were disobedient?
Heb. 3:19. So we see that they could not enter in because of unbelief.
Above he said: "was it not against those who sinned," but now: "the disobedient." He seems to be alluding to such believers from among the Hebrews, because many of them fell into other transgressions as well, besides faintheartedness and unbelief in the future. From this we see that the disobedient did not enter; that is, the punishment for sin is before our eyes and is acknowledged by all.