Matthew Poole and continuators on Hebrews 6:17

17 Wherein God willing more abundantly to shew unto the heirs of promise the immutability of his counsel , confirmed it by an oath .

The Apostle having stated the nature of an Oath in the antecedent, subjoins and applies it in a consequent, in which he shews that God sware to this end, that his own Counsel might appear to be Immutable, and the Consolation of Believers greater [non-Latin text not transcribed]; In which matter or case, viz. God's act of Promise and Oath to Abraham, it was not limited to his Person, but to all his Believing Seed, Rom. 4.23, 24. Out of his own meer Grace and free Will, his Goodness and Affection to them, without any consideration in them moving him, but his free, unexpected, as undeserved Mercy, did first Reveal, then Promise, then Swear: What more could he do? How liberal and abundant is his Love in these over-flowing discoveries of it? so to reveal and make known his gracious Thoughts, making them manifest, perspicuous and glorious, when none was privy to them, nor could reveal them but himself.

The Seed of Abraham's Faith, all true Believers, whom God had made Children and Heirs by Promise, as Isaac, Gal. 3.22, 26, 29. and 4.26, 27, 28. joint Heirs with Christ, Rom. 8.17. These alone did God intend to secure, and make certain of their Salvation.

God's unchangeableness in his Will and Decree, as in himself excludes all hesitancy, alteration or transposition of what it was from Eternity; God did never, will never change one Iota or Tittle of his Eternal Will and Decree of saving, perfecting and gathering into one, penitent Believers by the Promised Seed Jesus Christ, which he did reveal to the World, and without which manifestation, a Believer could have no Comfort, and without its Immutability, not any lasting and permanent Comfort.

[non-Latin text not transcribed] is proper for a Mediator, one who cometh in between two Parties as a Surety; and so is justly applicable to God the Son, who interposeth betwixt God the Father Promising, and Believers to whom the Promise is made, as Heirs, as a Surety engaging to see his Father's Promise made good to his Seed; and therefore confirms it to them with an Oath, that they might know the Promise was immutable, and should be punctually fulfilled; by which means he removes all doubts, fears, and jealousies about it from them. If they will believe Men who swear, how much more ought they to do so, and rest satisfied with the Oath of the Mediator.

Marginal references: Gr. Interposed himself by an Oath.