The book of Hebrews, from one perspective, is simply a long exhortation for professing Christians to persevere in faith until the end of their lives, to never abandon Christ. We have seen this already in Hebrews 3–4, as we are encouraged to enter God’s final rest through ongoing faith in Jesus, and calls to persevere will appear again in the epistle (e.g., 10:35–36; 12:1–2). Yet as we consider these exhortations, we must remember that we do not maintain our trust in Christ by our own power. Ultimately, the Lord brings about this perseverance, preserving us through His election of us unto salvation and the granting of effectual grace through the perfect work of Christ, grace that infallibly sustains us until the end (John 6:35–40; Rom. 8:29–30; Heb. 10:14). As the Puritan theologian John Owen comments on Hebrews 6:9–12, “Having freely adopted us, and made us heirs, it belongs unto [the] faithfulness and righteousness [of God] to preserve us unto our inheritance.”
God’s effectual grace, then, causes us to respond continually in faith and to produce the fruit of faith—obedience with the result that we persevere, imitating those saints who inherited the promise before Christ came (Heb. 6:9–12). Abraham ranks as perhaps the supreme example of such saints, so the author of Hebrews turns to Abraham’s life in today’s passage. For Abraham and for us, God’s promise and oath are two ways our Creator gives effectual grace. Specifically, the promise in view here is God’s promise to give Abraham many children, which we read about in Genesis 12:1–3; 15:1–5; 17:5; and 22:15–18. God confirmed this promise with an oath (Heb. 6:13–15), a reference to Genesis 22:16, which appears after Abraham proved his trust in God’s promise by being willing to sacrifice Isaac (Gen. 22:1–15). Abraham trusted God in perhaps the most arduous circumstances imaginable; so must we.
Yet, the Lord did not swear an oath by Himself to Abraham for the first time when He did so after the patriarch passed his test of faith. God first swore by Himself to give Abraham many children in Genesis 15 when He passed between the pieces of the animals. Essentially, He was saying to Abraham that He would be destroyed just like those animals if He were not to keep His promises to Abraham. God, of course, cannot be destroyed (Jer. 10:10), and since He cannot come to an end, this curse of destruction cannot fall on Him. And if the curse cannot fall on Him, He must keep His promise.