From Marx's Grundrisse: (it's short - think about it):
The communal substance of all commodities, i.e. their substance not as material stuff, as physical character, but their
communal substance as commodities and hence exchange values, is this, that they are objectified labour. [**] The only thing
distinct from objectified labour is non-objectified labour, labour which is still objectifying itself, labour as subjectivity.
Or, objectified labour, i.e. labour which is present in space, can also be opposed, as past labour, to labour which is present
in time. If it is to be present in time, alive, then it can be present only as the living subject, in which it exists as capacity,
as possibility; hence as worker. The only use value, therefore, which can form the opposite pole to capital is labour (to
be exact, value-creating, productive labour. This marginal remark is an anticipation; must first be developed, by and by.