Is it Jewish to believe in Jesus (Yeshua, his Hebrew name)?
One answer to this and other complex questions is simply that all those who have accepted Yeshua as the Messiah, and have accepted G-d's provision of atonement through him, remain Jewish. There is no conflict here.
History has come to know him as Jesus of Nazareth, but his friends and close associates just called him Yeshua ("salvation," see Isaiah 62:11). He brought a message of life, a message of hope and joy. He injected peace and purpose, meaning and significance into life after life. He has transformed us also.
"But," you might say, "doesn't Jesus, or Yeshua as you might call him, deny or oppose Judaism?" Not according to his own statements (Matthew 5:17-19), or according to the lives of his earliest followers, the apostles. They joyfully celebrated the holidays together and followed the Jewish traditions (Acts 2:46; 3:1; 20:5-6, 16; 21:24-26; 27:9). They came to realize the fullness that Yeshua said he would pack into their rich traditions. Even Rav Shaul, whom history knows as the Apostle Paul, remained a consistent, observant Jew (Acts 25:8; 28:17; cf. 21:20-26). Moreover, he claims that he continued to live as a Pharisee (Acts 23:6), among the strictest of the Jewish groups of the first century! History confirms this. Irenaeus, whose teachers were taught by the apostles themselves, described the apostles' lives (Against Heresies 3.23.15): "But they themselves...continued in the ancient observances...thus did the apostles...scrupulously act according to the dispensation of the Mosaic law." Even our best scholars, such as David Flusser of Hebrew University in Jerusalem, concur (Jesus, p. 216): "As a Jew Jesus fully accepted the law. The community he founded, comparable in some ways to the Essenes, saw itself as a movement of reform and fulfillment within Judaism, not as a secession from it."
Levi further reminds us that Yeshua did not come to abolish the law, but rather to fulfill it.
Yeshua was a Jew living in a Jewish land among Jewish people. All the apostles were Jewish as were the writers of the er Testament. For many years, faith in Yeshua was strictly a Jewish one. The book of Acts and other historical data tell us that during the first century there were hundreds of thousands of Messianic Jews. Moreover, there were Messianic Synagogues scattered throughout the Roman Empire and beyond. During this time, G-d miraculously showed his people that the Messiah was for both the Jew and the Gentile alike. Today, we are seeking to put the Messiah back into its biblical and Jewish context, and to share its beauty with other.