Is there any difference between Jews and Gentiles when they call on the Lord?

No, Scripture declares there is no difference between Jew and Gentile in this age of grace. The same Lord over all is rich unto all who call upon Him. Whether Jew or Greek, whosoever believes on Him shall not be ashamed. Salvation is open to all who call upon the Lord.

Les teaches from Romans 10 that there is no difference between the Jew and the Greek or Gentiles, for the same Lord over all is rich unto all that call upon Him. He notes that in the Old Testament, God primarily dealt with Israel, with exceptions like Jonah sent to Nineveh, Naaman the Syrian, and Ruth the Moabite. But now in this age of grace, it is flipped: God is primarily calling out Gentiles, but a few Jews, and the door is still open to them. Most Jews are blinded, yet the same Lord is rich unto all who call upon Him. So there is now no difference in this age of grace.

Romans 3

Why is there no difference between Jews and Gentiles in salvation today?

There is no difference because the same Lord over all is rich unto all who call upon Him. In this age of grace, salvation is by believing that Christ is the Son of God, died for our sins, was buried, and rose again; Jew and Gentile alike must come the same way.