Jesus was a Jew, the same way Paul, who brought Christianity, was a Jew. 
Same for Isaac, Jacob, Esau and so on.

On the eighth day of his birth, Isaac was circumcised, as was necessary for all males of Abraham's household to comply with the Jewish covenant. https://video.nostr.build/cfbea83c22ab7ce651a1e5c4c7d7eeb4132856293c2bc73f80eada5f96262e89.mp4 

 Jesus summarized his relationship to the Old Testament with this surprising statement in the Sermon on the Mount:

"Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them" (Matt. 5:17). https://video.nostr.build/7de9e177b8f8e9d5872cb46da713b7669897a1c2808f4fa999e5141451599278.mp4 

 Jesus was a circumcised jew who came to fulfill the old testament.

Matthew 5:17-18, Jesus declared, “Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.” Jesus’ mission to fulfill the Law. https://image.nostr.build/266c194629f5313575c9f409f59c1ca4379560ce0063f556e3c41089afbb971d.jpg