Hebrews 6:18 - Matthew Poole's English Annotations on the Holy Bible

That by two immutable things: another end of the Mediator's oath is here added, God's oath and a promise spoken to before, which are firm and stedfast to eternity; heaven and earth may pass away, but they cannot. In which it was impossible for God to lie, i.e. to cease to be himself, for essential truth to become a lie is impossible, it is utterly inconsistent with his nature. He is incapable to deceive, or speak against his mind, Numbers 23:19 1 Samuel 15:29 Psalms 89:35 Titus 1:2; and it is as impossible for him to violate his promise or oath. We might have a strong consolation; such as will vanquish all doubts, fears, jealousies, sorrows, distractions, putting the heart into a quiet, peaceful, settled frame, and stablishing it in it, whatsoever temptations, trials, or persecutions it may meet with from without or within to perplex it. Who have fled for refuge to lay hold upon the hope set before us: but it is the heart of a persevering believer, not of common professors, which is so strongly settled and comforted by them; such who flee to take hold of them; having cleared their right to them, and possessing their souls of them by faith, so to hold fast, as who would no more leave, than Joab would the horns of the altar, being a far greater security than it, or any city of refuge whatsoever; retreating to, and keeping in, this strong hold, nothing can interrupt their comfort. or hurt them, Job 13:15,16 Pr 18:10. The hope set before them is that eternal, good, and blessed state which is reserved in heaven for believers, the object of their hope set out to their view and prosecution as a prize in the promise, 1 Peter 1:3,4; by a metonymy of the effect for the cause, hope and good hoped for are joined together for our pursuit.