For a devotee or lover, the being, worshipped or loved, will always be the only one for her or him.
To change, to convert? Why bother?
During the Second World War, evacuated to non-Jewish households, I encountered Christianity at home and in school.
I was not comfortable worshipping another Jew.
I recovered my infant Judaism, but in a reformist version.
For a Christian, Jesus is the unique and only way that God has fully revealed himself. For a Jew this cannot be.