6:17

the heirs of the promise: Paul encourages the Hebrew Christians by reminding them of their connection to Abraham. God promised that faithful man that he would father an offspring that would bless “all nations of the earth.” (Ge 22:17, 18) As natural descendants of Abraham, the Jews were the first in line to inherit those promises. Most Jews rejected the Messiah, so they lost out on that inheritance. On the other hand, the Hebrew Christians did become “heirs of the promise”​—but not through their natural lineage. They became heirs by accepting Christ, the primary offspring of Abraham, and becoming his anointed followers. (See study note on Ga 3:29.) In time, all faithful Christians, including those with an earthly hope, would benefit from the promises God made to Abraham.

the unchangeableness of his purpose: The Greek word rendered “unchangeableness” in this verse and “unchangeable” in the following verse is one of several Greek legal terms that Paul uses in this context. (See study note on Heb 6:16.) The word here rendered “purpose” could include the idea of a person’s decision, resolve, intention, or will.​—See study note on Ac 20:27; see also study note on Eph 3:11, a verse in which a synonymous Greek term is rendered “purpose.”

he guaranteed it with an oath: When God made his promise to Abraham, “he swore by himself.” (Heb 6:13 and study note) Jehovah was not obliged to swear to the truthfulness of his promise, but he chose to do so in order to give humans absolute confidence in what he had promised. There could be no greater or more reassuring guarantee than his. The Greek verb rendered “he guaranteed it” could also convey the idea that “he stepped in” with an oath, confirming his promise. One reference work says that in this context, the word emphasizes “the validity of God’s promises. God is [the One who guarantees] . . . his own commitments.”​—See Glossary, “Oath.”