Why did God place a religious power in prophets, angels, and saints that enables them to perform miracles and makes it easy for them to fulfill people's desires and hopes, even though this is considered a greater cause for polytheism? And why do people's dreams and demands come true and their problems disappear merely by reading lines from the books of these individuals?

Allah does not grant prophets, angels, or saints inherent power to perform miracles. All creatures are weak and possess no power to benefit or harm themselves. The miracles that appear at the hands of prophets are by Allah's permission and will, solely to prove their prophethood, and are not evidence of their absolute power or to fulfill people's desires. Extraordinary occurrences that emanate from those other than prophets, such as charlatans and those who claim miraculous deeds (karamat), are actions of devils or mere lies and exaggerations, and a trial from Allah by which He distinguishes the true believer. A karamah differs from a miracle in that it is hidden and not for public display, and no one is sought for help except Allah, for Allah is the Self-Sufficient, and all creatures are dependent on Him.