Jesus was a Jew, and the Israelites are God’s chosen people, period. So they believe that God of the Old Testament is God. Christians believe in Jesus as God’s son, and the Holy Spirit given to Christians (ACTS) after Jesus died, resurrected, and ascended into heaven.
God is still God, and Jews worship only one part of him, but it’s still the same God.
Yikes. Okay, reverse that.
Christians believe that Jesus is God’s son. Jews believe that is nonsense, since their God doesn’t have sons, or Holy Ghosts, or the like.
Christians like to believe that their God is the God of the Jews, but that don’t make it so.