Have you even thought soap can be effective as a finish?

It is, and soap is really common wood finish in Denmark as well as other Scandinavian countries.

Soap and lye is used for priming of indoor woodwork. Treatment with lye soap prevents the wood from changing its color and enhances it making a bleach effect and when used on solid woods like oak, beech and pine may be a worthy experience.

By applying lye soaps, wood keeps its individual shade. This treatment prevents it from darkening and discoloration.

A soap finish is similar to a wax or oil finish, although it is so thin on the wood it appears like there's no finish at all. The wood soap finish is flat. There is no shine in comparison to oil and wax that do reflect light.

Regular maintenance is critical with a soap finish, even more so than with oil and wax finishes. For the first few months, soaped woods should be reapplied every few weeks, 2-3 times with a wood soap solution - the soap is very effective against dirt and even watermarks.

Dusting should be done with a moist cloth, never with furniture polish.