We Jews tend to see ourselves in a particular way. There’s a spectrum of Jewishness, with Haredi Jews at one end, secular Jews at the other, and the various shades of religiosity – Orthodox, Traditional, Progressive – situated in order between them. When Jews move across the spectrum, in either direction, we intuitively ‘know’ that they are becoming more or less observant, more or less assimilated, and we commonly judge them accordingly, often from our own vantage point on the spectrum.
There are empirical grounds upon which to justify this. Research consistently shows that progressive Jews score lower than orthodox ones on most standard measures of Jewishness, including their likelihood to attend a Passover seder, participate in Jewish community activities, feel part of the Jewish People, and give to Jewish charities. So, viewed in simple and generalised terms, the further to the religious ‘left’ people are, the less likely they are to be engaged in the particularities of Jewish life, and the more likely they are to acculturate to wider society.