""This nebula had such a resemblance to a comet in its form and brightness that I endeavored to find others, so that astronomers would not confuse these same nebulae with comets just beginning to shine." -Charles Messier
Astronomers have been scouring the skies for new discoveries since long before the invention of the telescope. Why, just with the naked eye and some dark skies, anyone can discover about 6,000 stars, five major planets, the Milky Way, and the occasional very faint nebula.
And of course, if you're very fortunate and very diligent, you could have been among the first to discover whenever a new comet brightened and suddenly appeared! By time comets get relatively close to the Sun, their tails become bright and extended, and often easily visible to the naked eye.
But the telescope changed everything. Because now, for the first time, you could discover a comet when it was still very faint. When it was, in fact, still invisible to the naked eye, but where a careful observer would notice an object where there previously was none. Something, perhaps, like 2004's Comet Machholz..."