If the wall fabric and finish is breathable, most of the water can easily evaporate, resulting in a relatively steady low moisture content of the walls. If the evaporation rate is higher than the water intake (e.g. by using breathable materials such as lime), the walls tend to stay relatively dry.
If the finishing is non-breathable and the evaporation of moisture is impeded (e.g. by using non-breathable materials such as cement), dampness gradually accumulates inside the building fabric, making the walls damper and damper over time.
The steady moisture content of the walls at any time depends on the ratio of water intake (water IN) vs evaporation (water OUT), which can have seasonal variations.
The moisture content of any given wall section is not uniform, but it varies. As a general rule, areas near the surface dry out more than deeper areas, where the effects of heating and ventilation can be insignificant.