“People of almost all religions try to convince other people to follow their respective religions. Why so?” That’s a significant thing to ask. You may be surprised: they are not really trying to convince others; by convincing others, they are trying to convince themselves that “We are not wrong.” When they are able to convince somebody, again they feel at ease: “My religion is right, I am not wrong. Look, even somebody who never belonged to my religion is convinced.” Christians go on converting people all over the world. The only reason is that THEY are not convinced of Christ yet.
The two most ancient religions in the world have been non-converting religions: the Jews and the Hindus. The Jews never converted anybody — they were so utterly convinced that there was no need to convince anybody else — the Hindus never tried to convince anybody. And these are the oldest religions in the world; in fact, all other religions are, in a sense, branches. Christianity and Islam are branches of Judaism; Jainism, Buddhism, and Sikhism are branches of Hinduism. The most ancient traditions have been non-converting. Why? The reason was that they were convinced; they were so ancient and they were not in need of new converts. Their very ancientness gave them enough ground to be convinced that they were right. Not that they were right, but they had this illusion of being right because of their long heritage going back into prehistoric times. They had the ancient most scriptures, and that was enough for them; that served their purpose.
But Christianity was a new religion; Christ had to start from ABC. Buddhism was new; Buddha had to start from abc. Mohammedanism was new; Mohammed had to start from ABC — he had nothing behind him to fall back upon. The only way for the Mohammedans was to convert others. They were substituting tradition by converting people and creating a great mass of followers; that was their way of convincing themselves. – Osho