Computer programs use interfaces to allow people to use them without reverting to symbols that are very hard to follow and are not understood by most people. So too Hashem left us interfaces that allow us to communicate with Him and to make His will manifest in this world. These are the Tzaddikim in every generation, whether they are righteous kings, prophets, sages of the Sanhedrin, or Torah leaders in their communities, their role is to execute Heavenly Providence.
But how do we know that they are really expressing Hashem's will and not their own? Although if they claim prophecy they have to accurately predict the exact date of a clearly positive event in the near future, several times. But that is not enough. They also have to live their lives in constant sincere quest of the Truth, their whole being has to be a receptacle for Heavenly desire. That is how the Tzaddikim live, continuously finding finer and finer flaws in their character, and fiercely eradicating them, till they have polished their personalities brightly and made them shine with an other-worldly light. Only then can we be sure that their will is not theirs.
Thus, the holy Torah exhorts us not to plant trees nor build buildings near the holy altar, for that which is near Him may have nothing else along with it, no edifices that aggrandize Man. Holiness and divine guidance require eradication of all foreign forms of worship, fearlessly combating any influence that does not surrender to holiness. Endless Heavenly bounty therefore comes down through those individuals who want nothing for themselves, only the minimum their duties require. Like fruit trees that grow to benefit others, so that they give and give like rivers of sweet water that does not stop.
Based on Rabbi Vali's book on Dvarim. Questions and subscriptions can be mailed to: the Yeshiva