17 Thus God, determining to show more abundantly to the heirs of promise the immutability of His counsel, confirmed it by an oath,
Verse 17 turns from human oaths to that of God’s oath that He swore to Abraham. He made it very clear to Abraham that His promise will be fulfilled.
17 Thus [in which]
“Thus” refers to the previous verse–the universal custom of human beings giving an oath to confirm something. God ratifies His promise as well. If a truth can be confirmed by an oath in human law, then it is even more certain when God gives an oath.
This verse shows why God confirmed His promise with an oath–His purpose was to make the unchanging nature of His purpose very apparent.
As men confirm what they say by and oath so God will accommodate Himself to an oath as well.
The word “determining” is from a Greek word meaning to desire something based on reason. God minded or reasoned to do what He did.
to show more abundantly
God shows “more abundantly” or much more by His oath than if He had not given an oath. His promise would have been enough, but He added an oath on top of it. The idea is that God is giving proof of what He said. It is a sworn affidavit.
to the heirs of promise
The “heirs” here include true believers in both the nation Israel and the church (Ga 3:29).
God’s messianic hope was not only for Jews but also for Christians.
God has made His promise/s to us patently clear. He condescended to human level to give assurance to His promise by an oath. This oath did not make the promise surer than it was before. The intention of the oath was to strengthen the faith of the believer. This demonstrated the unconditional nature of His promise. God will fully honor His oath. God Himself vouched for His promise. There were not two parties in this agreement, just one–God.
God not only makes a promise to the believer, but He also is the guarantor of the promise. God makes the promise and at the same time becomes the intermediary for the promise. God’s words should need no confirmation; His promises should be enough guarantee. However, by adding an oath to His promise He makes His promise certain; He makes it doubly sure. God’s oath made the unchanging nature of His purpose very clear. His oath provided an answer to doubt. God made a pledge to believers through the Holy Spirit (2 Co 1:22; 5:5; Eph 1:14).