In Paris he was a successful playwright, theater critic, poet, and essayist. Apart from original plays, he translated Goethe’s "Julius Caesar" into French. He increasingly turned, however, to Jewish subjects, while his poetry and thought were inspired by the Jewish mission, messianic inspiration, and the future of humanity. His plays also adopted Jewish motifs, such as his "Le Juif du Pape" about the meetings between the messianic kabbalist, Solomon Molcho and Pope Clement VII.
Apart from the period of World War I, when he served in the French Foreign Legion, Fleg wrote a series of works of Jewish interest, which proved highly influential among French Jewry and challenged its youth to think of their faith and spirituality. He translated Shalom Aleichem and the Passover Haggadah, and produced a monumental summary of Jewish thought in L'anthologie juive (which appeared in English in 1925). One of his major works of poetry was the verse cycle Ecoute Israel, which covered all Jewish history from the creation to the establishment of the State of Israel.
The Alfred Dreyfus affair, which unfolded while he was a student in Paris, and later the early Zionist congresses, as well as his friendship with the British writer, Israel Zangwill, all fostered in him a strong Jewish and Zionist orientation, and many of his writings were, in some way, answers to the questions he began to ask himself at that time.
I am a Jew because, born of Israel and having lost her, I have felt her live again in me, more living than myself.
I am a Jew because, born of Israel and having regained her, I wish her to live after me, more living than in myself.
I am a Jew because the faith of Israel demands of me no abdication of the mind.
I am a Jew because the faith of Israel requires of me all the devotion of my heart.
I am a Jew because in every place where suffering weeps, the Jew weeps.
I am a Jew because at every time when despair cries out, the Jew hopes.
I am a Jew because the word of Israel is the oldest and the newest.
I am a Jew because the promise of Israel is the universal promise.
I am a Jew because, for Israel, the world is not yet completed: men are completing it.
I am a Jew because, for Israel, Man is not created: men are creating him.
I am a Jew because, above the nations and Israel, Israel places man and his unity.
I am a Jew because, above man, image of the divine Unity, Israel places the divine unity, and its divinity.
Quotes from others about the person
During World War II, he left Paris for the south of France but refused an opportunity to find refuge in Switzerland. Years later, at a ceremony planting a forest in his honor in Israel, one of his assistants said, “You were always our spiritual leader but during the war, when you refused to leave us, you became, in scouting terms — our chief.”