You might wonder why your teachers seem so obsessed with vocabulary. As they prepare you for life after high school, they know that "learning the words is the same thing as learning the concepts." Seth Godin is a marketing genius. If you are good enough and lucky enough, you will work for a guy like him after you build the skill set he is looking for. Part of that skill set is basic literacy: reading, writing, and speaking well. In a recent blog post, he explains why vocabulary matters.
"Here's Randall Munroe's brilliant explanation of how the Saturn V rocket works. The brilliant part is that he illustrated it using only the 1,000 most common words (which, ironically, doesn't include the word 'thousand').
If you are only able to use 1,000 words, nuance goes out the window.
The typical native speaker knows 20,000 words, and there's your opportunity:
If you know 40,000 words, if you learn five words a day for a decade, the world changes. Your ability to see, to explain and to influence flies off the charts.
It's not about knowing needlessly fancy words (but it's often hard to know if the fancy word is needless until after you learn it). Your vocabulary reflects the way you think (and vice versa). It's tempting to read and write at the eighth-grade level, but there's a lot more leverage when you are able to use the right word in the right moment.
A fork in the road for most careers is what we choose to do when we confront a vocabulary (from finance, technology, psychology, literature...) that we don't understand. We can either demand that people dumb down their discourse (and fall behind) or we can learn the words.
It's hard to be a doctor or an engineer or key grip if you don't know what the words mean, because learning the words is the same thing as learning the concepts."