Two of the central theological themes of Christianity elucidated by Saint Augustine are fulfilment and conversion. Fulfilment in this respect mean the actualization of one's purpose. In Christianity, each individual was created for the explicit purpose of worshiping and loving God. Indeed, the world and the universe themselves were created to demonstrate God's glory and to worship Him through their very existence. Thus, fulfilment of purpose means coming into aliment with the deep, total, all-encompassing worship of God for which humans beings were created.
In Christian eschatology, other world religions are usually considered "partial" fulfillment's of mankind's ultimate purpose. Most Christian theological traditions hold that world religions such as Buddhism, Hinduism, Judaism, and Islam are important stepping stones in mankind's movement toward its ultimate purpose. Most (but not all) Christian traditions also posit that these faith traditions have something missing; something which only the central narrative of a resurrected Christ can provide.
Conversion is the process by which individuals come into full awareness of their purpose. Thus, conversion is an necessary prerequisite to fulfilment. Conversion happens at the individual level and also can occur at the global level. For example, in some Christian faith traditions, the Christ will reveal himself to all people, and all people will then accept him.
At both the individual and collective levels, conversion is necessary but not sufficient for the ultimate fulfilment of one's purpose.