When the music doesn’t feel quite major or minor, it might be in a mode.  What’s a mode?  Leonard Bernstein explains…

Bernstein was also greatly influenced by Jewish modes; the music that he heard growing up in his synagogue in Boston.

Bernstein particularly recalled an arrangement of the hymn Adon Olam (Lord of the World) that the music director of the synagogue, Solomon Braslavsky had composed, apparently for the high holidays. He described it as being of a complexity “not to be believed. Each stanza was a setting with organ interlude and great introductions. The basses would enter alone and then the sopranos – this is when I discovered that there was such a thing as counterpoint: great obbligatos floating from on high. ‘Arrangement’ is too small a word.  It was a great composition.  I knew every note of it because I heard it every year: it was like an opera.” (Humphrey Burton, pg. 9)

While I couldn’t find a recording of Braslavsky’s arrangement, this is the melody of Adon Olam.  I think Bernstein’s lyrical melodies (like the opening theme of the Serenade for example) might be unconsciously inspired by the spiraling melodies of ancient Hebrew hymns.  (And here, is a link to a different composition by Braslavsky.)

In fact, in a letter to Solomon Braslavsky, Bernstein wrote, “I have come to realize what I debt I owe to you – personally – for the marvelous music at Mishkan Tefila services. They surpass any that I have ever heard; and the memories I have of them are so bright, strong, and dear, that I shall probably never be able to estimate the real influence those sounds exerted on me.” (Letters  pg. 208)