The system of Presidential electors is a result of one of two critical impulses which influenced the Founding Fathers as they debated and refined what would become our Constitution. On the one hand, they were liberal advocates for representative government who earnestly believed that a polity was capable of taking their own governance in hand. On the other hand, that belief was tempered by a certain skepticism towards pure democracy, born of the fear that if given license to act as mobs, democracies would be torn apart by emotional and overwrought reactions. Consequently they sought to structure a government that balanced popular institutions with those controlled by more patrician influences. This is of course the general concept of separation of powers, which the Electoral College was thought to be a part of.

In Federalist no. 68 Alexander Hamilton actually addresses your question directly. He regarded separate electors to be an important buffer against the possibility of a President being selected according to a momentary whim or emotion on the part of the populace. By restricting the “immediate” election of the executive to “a small number of persons,” the system will “afford as little opportunity as possible to tumult and disorder” by forming an “intermediate body of electors” who “will be much less apt to convulse the community with any extraordinary or violent movements” because of their detachment from the passions which might govern the masses.

Furthermore, Alexander Hamilton felt that the federal structure would be a further guarantee against demagoguery or the undue influence of situational factors. Electors would be chosen specifically from and within a single state and not all together so that their division would render them less susceptible to “heats and ferments, which might be communicated from them to the people, than if they were all to be convened at one time, in one place.”

The electors’ transient station was also thought to have the ancillary benefit of helping to insure against the establishment of a “cabal, intrigue, and corruption” which might subvert the principle of representation which underlay the idea of elective government. You see, besides fearing the dangerous effects of unfettered popular influence, the Founding Fathers were also concerned that the nation might be suborned by an entrenched political class which existed to enrich itself and was vulnerable to foreign influence. To ensure that that should not transpire any “senator, representative, or other person holding a place of trust or profit under the United States” is excluded from being an elector.

The role of presidential elector was therefore very intentionally temporary. Because they had not made the “appointment of the President” dependent upon any “preexisting bodies of men (who might be tampered with beforehand to prostitute their votes),” they felt that they could ensure “that the immediate agents in the election will at least enter upon the task free from any sinister bias.” According to their reasoning, bribing a single elector or some number enough to exert undue influence would be simple enough if they held long standing office, but since effecting such corruption requires not only money but time as well, then “without corrupting the body of the people” the direct election of transient intermediaries that then select the President would be a sufficient safeguard against both mob-rule and corruption.

The ultimate goal of the Electoral College was to provide a conservative hedge against the manipulation of elections -- whether emotional or nefarious. Hamilton says it best, and at risk of straying too near to current political issues, I would quote him at length. He wrote:

“The process of election affords a moral certainty, that the office of President will never fall to the lot of any man who is not in an eminent degree endowed with the requisite qualifications. Talents for low intrigue, and the little arts of popularity, may alone suffice to elevate a man to the first honors in a single State; but it will require other talents, and a different kind of merit, to establish him in the esteem and confidence of the whole Union, or of so considerable a portion of it as would be necessary to make him a successful candidate for the distinguished office of President of the United States. It will not be too strong to say, that there will be a constant probability of seeing the station filled by characters pre-eminent for ability and virtue. And this will be thought no inconsiderable recommendation of the Constitution, by those who are able to estimate the share which the executive in every government must necessarily have in its good or ill administration. Though we cannot acquiesce in the political heresy of the poet who says: "For forms of government let fools contest That which is best administered is best,'' yet we may safely pronounce, that the true test of a good government is its aptitude and tendency to produce a good administration.”