When you tie Hebrews 6:18 in with the two verses before it and after it you find that it says that men swear and that ends the dispute, but God has sworn by Himself that and that is really the end of all disputes because God cannot lie. What has He sworn? He has sworn that we might have great comfort in the fact that he has set the hope before us that He has died and rose again and entered into the Presence of God. It is this hope because of His sacrifice in our place we don’t have to worry about our salvation. We who have sinned can flee into His presence for refuge (salvation and forgiveness). Plus, His being a forerunner (one who goes before to prepare a place) and a High Priest who always prays for us, it is that which shows we can be sure of our salvation and entering into the presence of God. The word hope in the Bible is one that means we can have confidence, not I hope so like we usually say it. This confidence in our salvation, forgiveness, and being able to enter into the presence of God is not because of us, but because of who He is and what He has done and nothing else. Do you have this confidence?
Hebrews 6:16-20 For men indeed swear by the greater, and an oath for confirmation is for them an end of all dispute. 17 Thus God, determining to show more abundantly to the heirs of promise the immutability of His counsel, confirmed it by an oath,18 That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us: 19 This hope we have as an anchor of the soul, both sure and steadfast, and which enters the Presence behind the veil, 20 where the forerunner has entered for us, even Jesus, having become High Priest forever according to the order of Melchizedek.