Are all unbelieving Jews under the Law? If they do not believe in Jesus, then how can we witness to Jews to believe He was the final sacrifice “to redeem those who were under the law....” as Galatians 4:5 says?
Paul tells us in Romans:
As Pastor Armstrong explains, the Law condemns a person for as long as they are under law. For a Jew who continues to practice the Law today (albeit in a very limited way), they are bound to the Law's requirements, which Paul says means they are forever under condemnation. But for the Jew who places faith in the work of Christ, that Jew comes out from under the penalty of Law. In this sense, all unbelieving Jews (who practice the Law) are under the Law.
Furthermore, the Law came as a part of a covenant, and that covenant is still in effect between Jesus and Israel, as Jesus Himself said:
The Law (and the covenant that delivered it to Israel) are still in effect until all that it requires is fulfilled. Jesus ultimately fulfills all of it on behalf of those who believe, and the fulfillment of that covenant for Israel doesn't happen until His Second Coming. So in that sense, the Jewish people are still "under" the covenant of Law. When an individual Jew believes in Jesus, that person comes out from under the covenant, but the rest of the (unbelieving) nation remains under that covenant for now.
In regard to Galatians 4, Paul was speaking about those who believe and therefore come out from under the Law (as he says in Romans 10):
Notice Paul says that Christ redeems those who "were" under the Law but by faith have now received the adoption as sons. So he's speaking about individuals who believe, not the entire nation of Jews.
Of course, any Jew who attempts to live under the Law is greatly limited in practice, since the priesthood and temple no longer exist. The writer of Hebrews says that the absence of these things in our age was intended as a sign to Israel that their covenant with God has been superseded by something greater:
The destruction of the temple was meant to be a sign to Israel that a new and better way to approach the Lord had been revealed in Jesus, so that for all who believe in Jesus they come out from under the condemnation of the Law.