One of the most important formulas you get out of electromagnetism is the coulomb force F = kQq/r^2 where k = 1/(4πε0), from that fact we define the electric field to be E = kQ/r^2, where you can notice the inverse square, 1/r^2 if you sketck the electric field R/r^3, it seems to be just divergent in any point but, when applying the formula of divergence, you'll be shocked that it's exactly zero, by the time the delta function was born it became widely known that this isn't quite true and ∇.(R/r^3) = δ3(r), r is the position, so ∇.E = 4πδ3(r)*kQ, by the definition of k ∇.E = Qδ3(r)/ε0, so ∫∫∫∇.EdV = ⊂∫∫⊃E.dS, this is the gauss's famous divergence theorem, ∫∫∫∇.E dV = Q/ε0*∫∫∫δ3(r)dV = Q/ε0*1, so the flux Φ = ⊂∫∫⊃E.dS = Q/ε0,Cheers