Why do we need the miracles of the Saints
Allah Most High has made the Holy Prophet (Sallallahu alaihi wa sallam), the last and final Prophet. Now there can be no Prophet. Until the Day of Judgment, everyone needs to believe in the Prophethood of the Holy Prophet (Sallallahu alaihi wa sallam). Obviously, for those who embrace Islam, these miracles of the Saints make them come closer to Islam and facilitate their acceptance of Islam. For this reason, the miracles of the saints of this Ummah are far more in number than the miracles of the saints of the previous Ummah.
Imam Yousuf Nabhani (May Allah shower His mercy on him) writes:
Translation: Allah Most High better knows the reason why the miracles of the Saints of the Ummah of the Holy Prophet (Sallallahu alaihi wa sallam) are in such a great number. One among them is that in the blessed life of the Holy Prophet (Sallallahu alaihi wa sallam) and after He passed away into the presence of Allah Most High, His superiority over all other Prophets has been well established. He is the Seal of all Prophets, the Beloved of the Lord Almighty and His religion is to remain until the Day of Judgment. For this reason, it is necessary that the signs that this religion is the true one have to be expressed in every era and among these authoritative proofs are the miracles of the Saints which are in reality the blessings of the Holy Prophet (Sallallahu alaihi wa sallam). (Muqaddima Jame’ Karamaat Ul Auliya, Pg. No. 36)
The Holy Quran mentions the pious people and saints at many places.