There is a familiar bumper sticker which reads, “God said it, I believe it, that settles it.” The bumper sticker is a tongue in cheek reminder that whatever God says is truthful because God is incapable of lying. So Christians have a hope in the assurance that whatever God says in His Word is going to be the same as at was yesterday and will be tomorrow. Of course there are people who don't see it that way, They say God's promises are open to interpretation or are no longer valid in today's society.
But as Numbers 23:19 clearly states, “God is not man, that he should lie, or a son of man, that he should change his mind. Has he said, and will he not do it? Or has he spoken, and will he not fulfill it?”
The writer of Hebrews, it appears, had a similar problem. The shallow faith of some of his fellow countrymen offered them no hope or assurance that God would keep His promises. In Hebrews chapter 6 he tries to take them from their simple,“Dairy Queen” like faith to a more substantial, “Longhorn Steakhouse” type of faith.
In Hebrews 6:13-18, he tells them God made a promise to Abraham which was sealed a few centuries later by the shed blood of His own son in order to redeem mankind.
And finally in Hebrews 6:19 -20, he tells them the matter of God not honoring His promises is settled because God would never consider breaking an oath He made at such a high price.
The writer of Hebrews explains in a few words the reason God took such pains to seal His promise is not because He had to but because He knows how susceptible humans are to fear and doubt. God knows even the smallest of trials can weaken the strongest faith.
And so, God didn't need to do anything but give His word but as an anchor for the hope each believer has in Christ Jesus, God swore His oath—to reassure all Christians throughout the ages from the time of the writing of Hebrews to the end of the age.
“Faith is a living, daring confidence in God's grace. It is so sure and certain that a man could stake his life on it a thousand times.” Martin Luther