6.1264 A meaningful proposition states something, and its proof shows that it is so; in logic every proposition is the form of a proof.
Every proposition of logic is a modus ponens presented in signs. (And one cannot express the modus ponens with a proposition.)
Modus ponens is argument of the form: If p then q, p, therefore q. Why is all logic just this in different forms? Why can’t this be expressed in a proposition? Perhaps because it is the general form that matters. What is p, after all, but a variable? Replace it with something specific and the general form goes away. But without such replacement, we don’t have a sinnvollen proposition.