O que significa a expressão "to play in the big leagues"

I guess most people or maybe everybody would agree working for a big company, like Google or Facebook, is a big dream come true. But one of these days, I read an article talking about the disadvantages of being a Google or Facebook employee. Among the many reasons, and I say many because they weren't few, one of them was having to deal with the fact that even being a renowned professional you may end up in charge of a very simple task. And that's reasonable if you stop to think even the janitor might hold a PhD. But imagine working for one of those major company is and will always be your lifelong dream. Here's what somebody might tell you as a piece of advice: You had better shape up if you want to play in the big leagues.

When you say the idiom "to play in the big leagues", you're alluding to playing a professional sport at the highest level. So the same way you'd do if you were part of a top-notch soccer team, if you want to succeed at something and play in the big leagues (that is to say, be involved in something of large and important proportions), you have to work really hard. That's all for today. Take care!