Why does the Bible say all people, Jew and Gentile, are shut up under sin?

Scripture concludes all people—Jew and Gentile—under sin because the whole human race is condemned as sinners and no one can keep the law perfectly to become righteous. This shuts everyone up to the promise given by faith in Jesus Christ to those who believe.

Les explains that if someone could keep the law in its entirety, they would be righteous enough for God's heaven, but no man can do it. Consequently, the whole human race is under condemnation as sinners. The Scripture hath concluded all, the whole human race, Jew and Gentile, under sin, so that the promise by faith of Jesus Christ might be given to them that believe. He also points out that believing is faith; faith is believing, so the two words become synonymous. Before faith came, we were kept under the law, and all the way back to Adam the one criterion for salvation for anybody was faith.

Ephesians 2:22

In whom ye also are builded together for an habitation of God through the Spirit.

What is the condition of the whole human race because no one can keep the law?

Because no one can keep the law in its entirety, the whole human race is under condemnation. Scripture concludes that all—both Jew and Gentile—are under sin, so every person is a sinner. The law cannot make anyone righteous enough for God's heaven; it only exposes universal guilt and the need for faith.