Below is an excerpt from "On Faith," an Internet feature sponsored by The Washington Post and Newsweek. Each week, more than 50 figures from the world of faith engage in a conversation about religion. This week, panel members were asked: Can you be critical of Israel and not be anti-Semitic? Can you be critical of Israel and be a faithful Jew?

In trying to discern how to distinguish legitimate prophetic criticisms of Israel from illegitimate ones, I have been greatly influenced by the words of Rabbi Jonathan in the Talmudic tractate of Tamid (28a): "He who reproves his neighbor with pure intent is worthy of a portion from God." Criticism, Rabbi Jonathan implies, must be carefully evaluated: Much depends on the motives of the critic.

The unworthy critics today are easy to find. Unlike the great biblical prophets, their shrill voices are neither moderated by love nor tinged with sadness. Their desire is to see the Jewish state destroyed.

The worthy critics, by contrast, are more scarce. Alive to the realities of contemporary Israel and the tragedies of the 20th century, their words mingle praise along with reproof. They speak directly, sadly, and always in pain. They are the rightful heirs of the biblical prophets, and the critics most worth heeding.

-- Jonathan D. Sarna, professor of American Jewish history, Brandeis UniversityTo read the complete essay and see more "On Faith" online commentary, hosted by Jon Meacham and Sally Quinn, go to http://newsweek.washingtonpost.com/onfaith.