Although during this scholarly phase of his life Imam Khomeini was not politically active, the nature of his studies, teachings, and writings revealed that he firmly believed from the beginning in political activism by clerics.
Three factors support this suggestion.
First, his interest in Islamic studies surpassed the bounds of traditional subjects of Islamic law (Sharia), jurisprudence (Fiqh), and principles (Usul) and the like. He was keenly interested in philosophy and ethics. Second, his teaching focused often on the overriding relevance of religion to practical social and political issues of the day.
Third, he was the first Iranian cleric to try to refute the outspoken advocacy of secularism in the 1940s. His now well-known book, Kashf-e Asrar (Discovery of Secrets) was a point by point refutation of Asrar-e Hezar Saleh (Secrets of a Thousand Years), a tract written by a disciple of Iran's leading anti-clerical historian, Ahmad Kasravi. Also he went from Qom to Tehran to listen to Ayatollah Hassan Modarres —the leader of the opposition majority in Iran's parliament during 1920s.
Imam Khomeini became a Marja in 1963, following the death of Grand Ayatollah Seyyed Hossein Borujerdi.
During November of 1964, Imam Khomeini made a denunciation of both the Shah and the United States, this time in response to the "capitulations" or diplomatic immunity granted to American military personnel in Iran by the Shah.
In Nov. 1964 Imam Khomeini was re-arrested and sent into exile.
Also this was a turning point in political viewpoint of Islam.
Reza Shah had transformed the Iranian monarchy into a modern dictatorship. The modernizing programs of Pahlavi dynasty restricted and threatened religious life and made clergies be against monarchy and finally Imam Khomeini decide to fight with them and build another state comparable to religious rules.