The house a transiting planet currently occupies is the area of life it is acting FROM — the domain supplying the impulse behind the contact.
Specifying the transiting house roots the contact in a concrete arena: the same aspect carries a different flavour depending on whether the transit is moving through your work, home, or partnership sector.
the life domain that is the source of the transit's pressure.
A transit moving through the 10th house pulls the contact toward career and public standing.