Accordingly God also, in His desire to show more convincingly and beyond doubt to those who were to inherit the promise the unchangeableness of His purpose and plan, intervened (mediated) with an oath. – Hebrews 6: 17 (AMP).
God confirmed his unchanging purpose to His heirs with an oath.
Who are His heirs? If you have accepted Christ, then you are an heir of God.
What is an oath? An oath is where you take a pledge in front of witnesses.
God made a covenant with Jesus that is stronger than a vow or pledge. His covenant is with Jesus. Neither of them will ever break the covenant.
Now that we are in Christ, nothing can stop us from receiving the benefits of that covenant…except our unbelief.
– Annagail Lynes