Abstract: The observation of gravitational waves has increased in regularity to the point it is almost routine. With LIGO's fourth observing run already underway, we are observing the most elusive objects in the universe multiple times per week. With NANOGrav recently announcing their first detection and new detectors, such as the recently adopted Laser Interferometer Space Antenna, coming online, this window into our universe is only becoming wider and clearer. Gravitational waves encode information about the sources that produced them and the nature of gravity itself. Decoding this information requires an understanding of general relativity and the gravitational waves compact objects could produce. Numerical relativity, computationally solving Einstein's equations, is the most accurate way to obtain such an understanding. Using numerical relativity together with gravitational wave data, we can listen to what the universe is telling us and probe the nature of gravity. This will become both more important and more challenging for high-sensitivity observatories. We must prepare now and leverage advanced technologies such as machine learning to take the foundational steps to ensuring numerical relativity is ready to capitalize on the wealth of data promised by next-generation gravitational-wave observatories.