Do I stop being Jewish if I believe in Yeshua?
No. You're Jewish by birth and covenant, and Yeshua is the Jewish Messiah. Many Messianic Jews keep Shabbat, the feasts and Jewish life, and say they feel more Jewish, not less.
Yeshua was born a Jew, kept the feasts, wore tzitzit (Matthew 9:20), taught in synagogues and the Temple, and died with "King of the Jews" written above him. His first followers didn't start a new religion; they believed Israel's Messiah had come.
Paul, after believing, still said "I am an Israelite" (Romans 11:1). In Acts 21 the Jerusalem believers were "zealous for the Torah".
Today there are Messianic Jewish congregations in Israel and around the world, where people pray in Hebrew, celebrate Passover and Yom Kippur, and follow Yeshua. Believing in him is about returning to the God of your fathers, not leaving your people.
Sources
- Luke 2:21-42 and 4:16-21; Matthew 9:20; Romans 11:1; Acts 21:20
