Why is it important that Jews who accept Christ be considered Jewish? And in what sense are they still Jewish?
Ethnically Jewish? But there are no pure ethnic Jews, or pure anyone, after 2,000 years of conversions (back and forth) and intermarriages.
Theologically Jewish? But those who follow Christ are Christians. Peter eventually referred to himself and others as Christian (1 Peter 4:16).
Because the faith was dejudaized. And the root of the faith is Jewish. Replacment Theology is unbiblical, Judizing is also unbiblical. Paul calls himself a Jew in all his letters as does Peter.