What is the focus of the passage?

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The postage stamp, which began as a piece of paper in token of a receipt of postage, has assumed additional functions. It is a mode of commemorating, celebrating and promoting national heritage and events. It plays a great role as an ambassador, a brand image of the postal administration and a statement of sovereignty of a nation. After independence, the medium of postage stamps in India was initially used to highlight the country's achievements in science and technology as well as its socio-economic development. In keeping with their dual character as a Token of Postage and as a Cultural Ambassador, there are two categories of stamps. The first is meant for day-to-day use as a token of payment of postage on mail articles. The second, on the other hand, are designed and printed with greater aesthetic inputs. They are manufactured in limited quantities and generate great interest among philatelists and collectors.