6:13 For when God made a promise to Abraham,
since he could swear by none greater, he swore by himself,
6:14 saying, "Most surely I will bless you, and I will surely multiply you."
6:15 Thus, having patiently endured, he obtained the promise.
 

6:16 For men indeed swear by a greater one,
and in every dispute of theirs the oath is final for confirmation.
6:17 In this way God, being determined to show more abundantly
to the heirs of the promise the immutability of his counsel, interposed with an oath;
6:18 that by two immutable things, in which it is impossible for God to lie,
we may have a strong encouragement,
who have fled for refuge to take hold of the hope set before us.

6:19 This hope we have as an anchor of the soul,
a hope both sure and steadfast and entering into that which is within the veil;
6:20 where as a forerunner Jesus entered for us,
having become a high priest forever after the order of Melchizedek. (Ps 110:4)

7:1 For this Melchizedek, king of Salem, priest of God Most High,
who met Abraham returning from the slaughter of the kings and blessed him,
7:2 to whom also Abraham divided a tenth part of all
(being first, by interpretation, king of righteousness,
and then also king of Salem, which is king of peace;
7:3 without father, without mother, without genealogy,
having neither beginning of days nor end of life, but made like the Son of God),
remains a priest continually.

7:4 Now consider how great this man was,
to whom even Abraham, the patriarch, gave a tenth out of the best spoils.
 

7:5 They indeed of the sons of Levi
who receive the priest's office
have a commandment to take tithes of the people according to the law,
that is, of their brothers, though these have come out of the loins of Abraham,

7:6 but he whose genealogy is not counted from them has taken tithes of Abraham,
and has blessed him who has the promises.
7:7 But without any dispute the less is blessed by the better.

7:8 Here people who die receive tithes,
but there one receives tithes of whom it is testified that he lives.

7:9 So to say, through Abraham even Levi, who receives tithes, has paid tithes,
7:10 for he was yet in the loins of his father when Melchizedek met him.

When God makes a promise, it is as if He creates a rock so big that not even He can move it. For if He doesn't keep His promise, He violates His own character.

If a believer in Christ is denied access to heaven, then God shows Himself to be a liar.

But since it's impossible for God to lie, then the believer has a secure anticipation of entering heaven, which is the reason why God made a big deal about making an oath, so that our confidence would be based on His unchangable character.

• Combines the roles of King and Priest
• Genetic origin irrelevant
• Aaron submitted to Melchizedek through Abraham