How Mantras get their powers?

How does mantra get its powers? How does it generate positive imprints on our mind? Many Buddhists explain it by saying that while we recite the mantras, our mind is turned away from committing anything negative and thus planting good causes for the future. However this does not explain how mantras by itself is able to generate so much postivie potential. It doesnot explain how mantras get its "magic". Many people just explain it by the fact that mantras are the Buddha's words. Recently while studying Shin Buddhism, I got the answer I need on how names and mantras got their inconceivable powers.

Well, take medicine Buddha's mantra for example. If it doesnot heal a person, at the least it is said to be able to build positive merits in the person by hearing or reciting it. And why this is so? It is because of the Buddha's vows associated with the mantras. It functions in inconceivable ways just like how the Vows (especially the 18th Vow) of Amitabha Buddha works in taking sentient beings to his Pure Land. They made these vows to help sentient beings when they were in the causal ground, and now that they are Buddhas, the vows take enormous potential in helping sentient beings, including the vows in the form of mantras. Before Dharmakara became Amitabha Buddha, he cultivated for 5 long kalpas and hence he infused his Vows by that much length of time. That's why reciting Amitabha's name is so effective. Same for his mantra. His mantra is linked to his vows.

That's also why while we are in the causal ground, in the Mahayana we are taught that we should learn to make great vows like these Buddhas did. Then when there is a mantra associated with you, when you become a Buddha, it will have enormous potential too. Hence, not only does doing certain actions (such as offerings of food to monks, donating money to charity, etc) bring merits, reciting mantras too creates postive merits!