Seeds germinate once they become moist, but they need the correct temperature and light conditions too.

Soil shouldn't become waterlogged or dry out.

The root grows first and has to be able to push through the soil while absorbing water and nutrients via the fine root hairs. So the seedbed shouldn't be rock solid (from trampling or baking hot weather), or cloddy, because the roots can't make contact with the soil but are left in the air spaces between.