Hebrews 6:17-18 (ESV)
So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath,  so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us.
Psalm 103:14 is a stupendous piece of truth. It says that God remembers that we are dust. The eternal Father who can do whatever He pleases remembers that we cannot. It is never out of His sight that we are temporal, frail, ignorant, doubtful, uncertain, liable to pain and easily destroyed, easily distracted and easily fooled. And the fact that He remembers it means that He is concerned for us. He will use His resources for our good. He will speak to us in ways that we can understand. He will bring Himself to our level and communicate understandably. He who is incomprehensible will make Himself to be understood.
And this is what we encounter in Hebrews 6:17. God makes a promise to the Old Testament patriarchs (this most likely is the renewal of the covenant to Abraham in Genesis 15) and confirms it with an oath in order to show them the unchangeable character of His purpose.
Astounding. All God had to do was say “I am God and you have no need to question me. Now sit down and be quiet.” But He did not. He made a promise and to accommodate those to whom the promise was made He confirmed it with an oath. He remembers that even the patriarchs are made of dust. He is conscious of the weakness of man’s faith and to help them have confidence in what He has promised He uses a human instrument of guarantee.
But this does not just have implications for the original recipients of the promise. Because of God confirming the covenant by two unchangeable things – His word and His oath, verse 18 says that we now have a strong encouragement to hold fast to the hope set before us. All who believe are children of Abraham (Galatians 3:7) and the confirmed promise is as much ours as it was Abraham’s.
Have you fled to God for refuge from the due penalty of your sin? Have you fled to Him for salvation? Are you trusting Him to do for you what you cannot do for yourself? He turns none away who flee to Him. You can have the same encouragement that Abraham had. Doubt yourself if you must, but you need never doubt the Word of the One who promised to save you and confirmed it with an oath.
What a liberating thing this is!! Get on with the business of living for the praise of God’s glory. He has you. You do not need to stare at your navel and wonder if He will save you. Go live for God. Attempt great things for God for He has promised to grant you far greater than you will ever do for Him. Your faith is as secure as the promises of God. And that makes all other security look pretty fragile. Wrestle in His power for He uses it for you.