As the NYT points out, Hadewijch has to leave the monastery before she can become a true extremist.
Via NYT:
The film repeatedly seeks to evoke that contradictory sense of connection and alienation, not only in fervent Christianity but also in Islam, and it examines how the relentless pursuit of ultimate faith drives people to violent acts that are public manifestations of self-mortification.
(...)
Céline, having returned to secular life, is befriended by Yassine (Yassine Salime), a young Arab layabout who lives with his older brother, Nassir (Karl Sarafidis), in the projects on the fringe of Paris. Her curiosity about Islam prompts Nassir to invite her to a discussion group on “the notion of the invisible,” and they embark on a protracted dialogue on religious faith in which Nassir speaks abstractly of violence and “the fight.”
Typical of a film by Mr. Dumont, “Hadewijch” makes sudden leaps without filling in the details. After Céline rebuffs the advances of Yassine, who calls her “nuts,” Nassir becomes her spiritual mentor, and they travel to an unidentified Middle Eastern country (the sequence was filmed in Lebanon), where they arrive just after a bombing. Céline is shown having tea with the members of what appears to be a terrorist group and swearing to carry out some unspecified mission. Then she is back in France.
Periodically, the movie focuses on David (David Dewaele), a gaunt young parolee working on the monastery property who observes Céline’s comings and goings. His presence remains mysterious until the very end, when he becomes an ambiguous redemptive symbol who “saves” Céline after she has committed two desperate acts.
“Hadewijch” and the forthcoming “Of Gods and Men” (shown at this year’s New York Film Festival) suggest that for all the talk of France’s metamorphosis into a secular society, powerful religious and spiritual fires still burn there.(source)