It is assumed that light does not propagate through a different medium as such but by interacting with electrons of atoms it reaches. So photons crash into electrons of the medium's atoms, elevate their energy level and when falling back to their original energy level, they themselves create photons of the wavelength h/E. The question is: what about direction? Let's say the point source is a laser whose photons pass through a glass, why does it not scatter everywhere as the electrons falling back emit photons in 360° x 180° direction?
Glass typically has a very high bandgap due to its low refractive index so photons of visual wavelengths typically don't have enough energy to cause the excitation of electrons in glass since the photons would require an energy $\geq E_g$. Thus, the photons are simply transmitted through the glass since they don't have enough energy to interact with the electrons, and the direction and angle can be described with the refractive index.
Beside this, one can also discuss the topic of scattering, which can be quite complex if one wants it to be. Shortly put, the roughness of a surface quantifies the angle at which we'll observe scattered photons. Worst case would be Lambertian scattering, where it is scattered in all directions in a half-sphere and best case would be no scattering but only transmission.