We use mass as a property of objects that relates to the deformation that this object causes into the field that embeds this object. In black holes the scale of its boundary is proportional to its mass. For spherical black holes this means that their mass is proportional to their radius.
Far from a massive object with mass m, the gravitation potential of the object g(r) equals g(r)≈ mG/r
The shape of the Green's function of the field is f(r)=1/r
This means that a relation exists between the Green's function and the gravitation potential at far enough distance r
The Green's function has some volume and the spherical black hole also has some volume. If the volume of an extra Green's function is added to the black hole, then that volume is added to the volume of the black hole in an isotropic way. Its radius appears to scale with the number of added Green's function volumes.
This raises the idea that the internals of the black hole are optimally filled with Green's function volumes and that the mass of the black hole is proportional to the number of Green's functions that in this way determines the volume of the black hole.
Spherical pulse responses can inject the volume of the Green's function into a field. Thus, when the injection takes place within the internals of a black hole, then the scaling rule becomes manifest.
Spherical pulse responses act as spherical shock fronts. The above story implies that spherical shock fronts cannot pass the boundary of a black hole. That boundary is known as the event horizon.
Usually the event horizon is interpreted as the place where the escape velocity equals the light speed or as the place where the energy of a photon equals the gravitational energy.