It is, my good CG, possibly purely arbitrary. It may just as well have been B, L, N, F, S, H, D, T, C, M, G, Ng, R... or F, U, Þ, A, R, K, W, H, N, I, J, E, P, Z, S, T, B, E*, M, L, Ng, O, D. On the other hand, it may have had some mystical significance to the ancient Semites and have suffered only minor modifications by the poor benighted, unenlightened Greeks and Romans.

*Yes, I know there are two Es in here. They're different Es.