"The Gospel as a document of history". In Judaism and Christianity / Leo Baeck. Philadelphia : Jewish Publication Society of America, 1958. p. 101-102.
This man could have developed as he came to be only on the soil of Judaism; and only on this soil, too, could he find his disciples and followers as they were. Here alone, in this Jewish sphere, in this Jewish atmosphere of trust and longing, could this man live his life and meet his death—a Jew among Jews. Jewish history and Jewish reflection may not pass him by nor ignore him. Since he was, no time has been without him; nor has there been a time which was not challenged by the epoch that would consider him its starting point.
When this old tradition confronts us in this manner, then the Gospel, which was originally something Jewish, becomes a book—and certainly not a minor work—within Jewish literature. This is not because, or not only because, it contains sentences which also appear in the same or a similar form in the Jewish works of that time. Nor is it such—in fact, it is even less so—because the Hebrew or Aramaic breaks again and again through the word forms and sentence formations of the Greek translation. Rather it is a Jewish book because—by all means and entirely because—the pure air of which it is full and which it breathes is that of the Holy Scriptures; because a Jewish spirit, and none other, lives in it; because Jewish faith and Jewish hope, Jewish suffering and Jewish distress, Jewish knowledge and Jewish expectations, and these alone, resound through it—a Jewish book in the midst of Jewish books. Judaism may not pass it by, nor mistake it, nor wish to give up all claims here. Here, too, Judaism should comprehend and take note of what is its own.