Starting from Maxwell's equations, \begin{align} \nabla \cdot \vec{E} & = \frac{\rho}{\epsilon_0} & \nabla \cdot \vec{B} & = 0 \\ \nabla \times \vec{E} & = - \frac{\partial \vec{B}}{\partial t} & \nabla \times \vec{B} & = \mu_0 \vec{J} + \mu_0 \epsilon_0 \frac{\partial \vec{E}}{\partial t} \end{align} it is standard practice in any electromagnetism course to derive a wave equation to show that waves propagate through these fields, and that light is that wave. Simplifications are frequently made, like using the vector potential or looking at the homogeneous case ($\rho = 0$ and $\vec{J} = 0$).
The inhomogeneous wave equation for $\vec{B}$ is fairly straightforward to produce and interpret (take the time derivative of the $\nabla \times \vec{E}$ equation, then substitute for $\frac{\partial \vec{E}}{\partial t}$ by solving for it in the $\nabla \times \vec{B}$ equation). After using the fact that $\nabla\cdot \vec{B} = 0$ you get: $$\frac{1}{c^2}\frac{\partial^2 \vec{B}}{\partial t^2} - \nabla^2 \vec{B}= \mu_0 \nabla \times \vec{J},$$ a nice, clean, wave equation that has $\nabla \times \vec{J}$ as the source term.
With the wave equation for $\vec{E}$, though, things don't look as clean. Just reverse the order of how the two curl equations were manipulated to get the $\vec{B}$ wave equation to get $$\frac{1}{c^2}\frac{\partial^2 \vec{E}}{\partial t^2} - \nabla^2 \vec{E} = -\frac{1}{\epsilon_0}\nabla \rho - \mu_0 \frac{\partial \vec{J}}{\partial t}.$$
Again, a nice, clean wave equation, but this time I'm finding the source term harder to interpret from a physical point of view. In terms of special relativistic tensors, we can render both equations as a single equation to be $$\partial_\alpha \partial^\alpha F_{\mu\nu} = \mu_0 \eta_{\nu\alpha} \partial_\mu J^\alpha - \mu_0 \eta_{\mu\alpha}\partial_\nu J^\alpha ,$$ where $J^0 \equiv c\rho$, and $\operatorname{sig}(\eta_{\mu\nu}) = (+,-,-,-)$. This suggests that the right hand side of the $\vec{E}$ wave equation is part of the $4$-dimensional generalization of the curl - specifically the mixed (time-like, space-like) components of an anti-symmetric tensor formed with $J^\mu$ and $\frac{\partial}{\partial x^\nu}$. The pure space-like parts of that tensor are easy to visualize because studying E&M gives lots of practice working with ordinary curls (a tendency of a vector field to circulate around a point). Is there a similarly intuitive and visualizable description for $$\frac{\partial J^0}{\partial x^i} + \frac{\partial J^i}{\partial x^0}?$$