Why the aperture and focal length of objective of a telescope are large?

The aperture of a telescope is large to collect more light, which enhances the clarity and brightness of the observed images, especially for faint celestial objects. A larger aperture also allows for better resolution, enabling the telescope to distinguish fine details in astronomical objects. The focal length, on the other hand, is large to provide higher magnification and to create a more detailed image by allowing better separation of closely spaced objects. Together, these characteristics improve the overall performance and effectiveness of the telescope in astronomical observations.