Both Uses of

expedient
in
The House of the Seven Gables

Hence, too, might be drawn a weighty lesson from the little-regarded truth, that the act of the passing generation is the germ which may and must produce good or evil fruit in a far-distant time; that, together with the seed of the merely temporary crop, which mortals term expediency, they inevitably sow the acorns of a more enduring growth, which may darkly overshadow their posterity.†
Chpt 1

expediency = convenient, speedy, or practical; or an action that is speedy or practical

Not improbably he was the best workman of his time; or, perhaps, the Colonel thought it expedient, or was impelled by some better feeling, thus openly to cast aside all animosity against the race of his fallen antagonist.
Chpt 1 *

expedient = convenient, speedy, or practical

Definitions:

(1) (expedient)
convenient and practical, but sometimes not the best or most moral choice
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely, expedient can also imply that an action was taken for reasons of self-interest rather than for moral reasons.

In the sense of speedy, the word is less commonly used today than in the past; though it may still be used as in "an expedient end" or "an expedient amount of time," or "We are depending upon your expediency."