When learning calculus, it is important to keep in mind all the important concepts in previous math courses. Things such as trigonometry, functions of multiple variables, vectors, and algebra become extremely important. Calculus itself is not that difficult (despite its reputation). Its just that you need a lot of previous math background to be able to learn it successfully.
After learning calculus, you soon learn how much of the scientific world you have been missing out on without it. All those physics equations you learned in high school? They're just simplifications made that only apply in very specific situations without. With calculus, you can apply physics to almost any situation you can imagine. The vast wonders of the universe become accessible to you with a relatively simple mathematical background.