This, as quoted by Stephen was a history lesson and a reminder that they had not always followed God's law. Later in this very section it is pointed out that godly Jews buried him. Acts 7:58 And cast him out of the city, and stoned him: and the witnesses laid down their clothes at a young man's feet, whose name was Saul.

And they stoned Stephen, calling upon God, and saying, Lord Jesus, receive my spirit,

And he kneeled down, and cried with a loud voice, Lord, lay not this sin to their charge. And when he had said this, he fell asleep.

And Saul was consenting unto his death. And at that time there was a great persecution against the church which was at Jerusalem; and they were all scattered abroad throughout the regions of Judaea and Samaria, except the apostles.

And devout men carried Stephen to his burial, and made great lamentation over him.

As for Saul, he made havock of the church, entering into every house, and haling men and women committed them to prison.

The promises don't apply unbelieving Jews. They apply to those who have been baptized into Jesus Christ.

Romans 3 answers this quite nicely: https://www.blueletterbible.org/kjv/rom/3/1/s_1049001

This Is not entirely accurate, please read Romans 9 - 11 with an open mind. https://www.blueletterbible.org/kjv/rom/9/1/s_1055001,