The E39 BMW M5 is an important car for BMW for a number of reasons. First, it is widely regarded as one of the best sports sedans ever made, offering a perfect balance of performance, luxury, and practicality. Second, it was the first M5 to be powered by a naturally aspirated V8 engine, which has since become a hallmark of the M5 lineup. Third, it was a critical and commercial success, helping to establish BMW as one of the leading manufacturers of high-performance cars.