Jesus was a Jew.
That statement catches many Christians (that is, followers of Jesus) off guard. It is easy to label Jesus, since he is the impetus for Christianity, as a Christian, even though his time spent on earth was as a Jew.
Indeed, he was born a Jew, into a Jewish culture, and had a clear Jewish lineage. He was raised and educated in Jewish beliefs and traditions. His ministry was primarily to Jewish people (though he certainly ministered to non-Jews and made it clear that his message was for all people, his focus was the Jews). Plus, most of his disciples were Jews, as presumably were most of his followers. In fact, initially Christianity was viewed as a sect of Judaism. [Acts 28:22]
Yes, Jesus was Jewish.
As such, there is much that his followers owe to and can learn from Jewish traditions and beliefs. This is one important reason to study the Old Testament and to embrace our common ground with our Jewish bothers and sisters.