Not "temporily shut down". Fulfilled.
All the promises were fulfilled in Christ Jesus. Those who have faith are the heirs to the promise.
(Gal 3:29) If you belong to Christ, then you are Abraham’s seed, and heirs according to the promise.
All that is, is what Paul began the chapter with - the issue of inheritance of eternal life that righteousness through faith allows.
A promise fulfilled, or made possible by the Cross.
Back when Abraham was promised he would be the father of many nations (content of that gospel or good news preached unto Abraham), he believed God and God counted his faith in said gospel from God, He counted his having believed God, unto him for righteousness.
Paul's point being that whomever believes the content of God's good news unto him; God counts their faith unto them for righteousness, just as He had done with Abraham.
Paul is laying out a timeless Principle that is at the same time Dispensational.
That differs as to the content of the message to the particular individuals within the particular Dispensation that they are expected to believe.
Just as this had once been a gospel or good news and accompanying set of related instructions as to one's required expression of faith, that had once been on the table...
Deuteronomy 6:24 And the LORD commanded us to do all these statutes, to fear the LORD our God, for our good always, that he might preserve us alive, as it is at this day. 6:25 And it shall be our righteousness, if we observe to do all these commandments before the LORD our God, as he hath commanded us.
And that; towards its' intended result...
Romans 3:19 Now we know that what things soever the law saith, it saith to them who are under the law: that every mouth may be stopped, and all the world may become guilty before God. 3:20 Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
In contrast to that gospel, is this one...
3:21 But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets; 3:22 Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference: 3:23 For all have sinned, and come short of the glory of God; 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus: 3:25 Whom God hath set forth to be a propitiation through faith in his blood, to declare his righteousness for the remission of sins that are past, through the forbearance of God; 3:26 To declare, I say, at this time his righteousness: that he might be just, and the justifier of him which believeth in Jesus.
Duh-uh - you're as confused about Galatians as the 28ers and 9/28er Hybrids are.