Some guy who lived several decades after the time of Christ may or may not have given his opinion on this subject. We have no idea whether Barnabas actually existed, whether he actually wrote his epistle, or whether it was written by someone else and attributed to him.
How is this proof of anything other than a 2,000 year old manuscript says something you agree with?
That belief aka supersessionism was the default interpretation of the Bible until the 1930s-40s when jews started lobbying churches to claims jews were still chosen. Almost all churches on Earth then fell in line.
most Christians are really just jew worshipers and members of the blood cult. It means submitting to an international jew banking system which makes every pseudo-Christian complicit in the evil of the regime which is under the guise of zionism. Zionism is the jewish intention to bring about the anti-Christ and for some reason these pseudo-Christians are compelled to assist them despite proclaiming Christ. They also have trauma spaces in their brain because they had their penises butchered because jews like to take the skin off the tip of the penis and say it is for health or something. It's all sick black magick stuff but most Christians are not really untethered from the devil system.
How is this proof of anything other than a 2,000 year old manuscript says something you agree with?