Papers (essays and such like) are written for a specific class and based on your current knowledge. So, it makes sense that a later paper (for a more advanced class) would contain different -- more current) information than the one done earlier. If the earlier paper got you, say, an A, then it very likely will get you a C (or at most a B) in a later course. Or a D or F if you had only achieved a B
So, it might not be plagiarism to hand in the same essay, but it suggests that you have learned nothing in the advanced class.