Generally I have found that this "vendutal" is not as simple as is being made out in the posts here. I am aware of a number of cases where the concerned devotees (those who do a ceratin "vendutal" in respect of a particular episode - like job selection in a particular interview, marriage with a certain boy/girl, etc.) performing the same even though they were not successful in that particular attempt but some other interview, marriage, etc., would be successful subsequently and then they will say, "see, that particular job/marriage would not have been good for us, that was why god did not allow it; now this is what is having "deivaanugraham" and so we should perform the venduthal. Deivakkadan baakki irukkapadaathu, kudumbatthukku dosham."
I have also seen cases where divination ("prasnam" in Kerala side) brought out some venduthal kadan or deiva kadan as cause for current problems, some expert astrologers were able to nearly pinpoint the venduthal and then the concerned parties remembered one such examples as cited above by me. When the people concerned tried to say that the particular marriage, job etc., did not transpire, so why should there be a compulsion to perform it, the answer given by the astrologers is more or less on the same lines given. ("see, that particular job/marriage would not have been good for you, that was why god did not allow it; now later on it did happen and that is what is having "deivaanugraham" and so you ought to perform it.")
Though I would prefer people to refrain from "Manotis" as the northerners say, I do not think it is possible to lessen it. (It is as difficult to remove maayaa from Brahman, in the advaita philosophy!) The devotees probably feel that whatever they lack on their personal efforts, will be made good by some superior force which is identified with a particular deity and temple and then they solemnly swear to do some venduthal, as a symbol of their sacrifice, so that the help of that superior force may be available to them at the nick of time in ever so many ways so that their deficiencies are made good and their objective is achieved.
Here, the objective is as much materialistic as say, in any of the yagas or other sacrificial rites of the vedas. "You perform a certain "sacrifice" and you will get such-and-such benefit", take putrakameshti, rajasuyam, or whatever. Change this philosophy a bit and it becomes, "If I get such-and-such benefit, I swear I will perform a certain sacrifice."
I would speculate the reason for the common folks standing the vedic priests' postulate on its head, to be the solid, earthy, commonsense of our ordinary, illiterate folks. They were not probably too convinced about the original dictum and its infallibility but, nevertheless, were not averse to giving it a try in times of extreme need and urgency. Hence they changed it into a certain reverse contract, which now looks like "bribing god". In some ways the yagas (vedic sacrifices) were also a mirror image of such venduthals, IMO. So, if we want to remove one, the other also would need to be removed.
Lastly, Gita III, 11 and 12 do appear to encourage "the people and the devas to nourish each other" and "thus nourishing each other, you will attain the highest good."
devān bhāvayata anena te devā bhāvayantu vaḥ |
parasparaṃ bhāvayantaḥ śreya: paramavāpsyatha ||
May be this was interpreted to mean that by mutual give and take, gods and the dvijas will both achieve their goals.
