This is where the action is. There are only 100 senators in the entire country (two for each of our fifty states), and every single one has the ability to create and oppose every single law the government decides we need (or don't need). In other words, you have the power to change the lives of 300 million or so people—even if some days you're so stressed out you can't decide between paper or plastic at the grocery store.
You aren't the most powerful person in America, but you do exist to help balance out that person's power. Unless your teachers in school did an absolutely terrible job, you hopefully know that we live under a three-part government, with each branch existing to check the power of the other branches. The POTUS (President of The United States) can't do much without the very elite membership of the Senate.
Thanks to governmental rules that are far too complex to explain in one tiny section of profile, he or she will typically need two-thirds of the body's members to vote for something they want done, like the appointment of federal employees such as judges or the passing of a bill.
This means that they need your vote. To have the Leader of the Free World call you personally to ask (beg) that you vote for something they want is a ridiculous amount of power to hold. Will you say yes or no? It all depends on how nicely they ask.