As we discovered in a study of Ruth, Nehemiah and Ezra, the returning exiles were urged to keep themselves pure and free from Gentile contacts. This was considered necessary in order to preserve the purity of Judaism, but among those of a more liberal viewpoint there was probably a recognition that non-Jewish people too had a part to play in God's purposes for mankind.
It may well be that this little book is a gentle protest, for
in it God is represented as rebuking "Jonah" (= "Dove",
another name for Israel) for his lack of concern and compassion
for the Gentile city of Nineveh.
Jonah 1.v.1 to 4.v.11
(As the whole of this short book is recommended here, no hyperlinks are used - PN)