Calling upon the Prophet and the imams (also referred to as istighathat al-nabi wal-a'immah) is allegorical, not literal. The Noble Quran teaches people to worship and seek help from Allah (”iyyaka na'budu wa iyyaka nasta'in”); however, the allegorical seeking of help is permitted in the Noble Quran. For example, in the story of Prophet Musa (Moses), “And he found there two men fighting—one from his party (Shi'a), and the other from his foes. The man of his own party asked him (istighathahu) for help against his foe, so Musa struck him with his fist and killed him.”
Many of the narrators of hadith narrate a prayer (du΄a) from the Prophet which begins, “O my Lord! I turn to you by your Prophet, the Prophet of Mercy (Allahumma, inni atawajjahu ilayka bi nabiyyika nabi al-rahma…).” Then it says, “O Muhammad! I turn to Allah by you to solve my difficulties.”
It is also narrated that the feet of 'Abdullah ibn Umar al-Khattab became disabled and he could no longer walk. After being told to call upon the closest people to his heart, he said, ”Wa Muhammada!” His feet became cured and worked properly again. The Noble Quran teaches us to “seek help through patience and prayer (sabr and salat).” Sabr (according to commentators of the Quran, in this context refers to fasting) and salat (prayers) are means which ultimately lead one to Allah. Thus calling upon the Prophet or Imam Ali is allegorical since all agree that Allah is the main source of support, aid, and assistance and they are just a means to Him.
Some Muslims associate calling upon the Prophet or the imams as shirk (heresy). They argue that a person should not ask any person for help. However, we see that if a person is faced with a problem in life, often, this person will logically and naturally call upon a nearby person for help. If a person was about to drown and he called out for help, then would his seeking help from someone other than Allah make him a mushrik (associating one with Allah)? By the same reasoning, calling upon the Prophet or the imams is not shirk. The argument that they cannot be called upon because they are dead is also invalid, because the Quran falsifies the notion of martyrs being classified as dead, “Think not of those who are killed in the way of Allah as dead. Nay, they are alive with their Lord, and they have provision.” “And say not of those who are killed in the way of Allah, 'They are dead.' Nay, they are living, but you perceive it not.” If an ordinary Muslim was martyred (for the cause of Allah) is considered to be alive, then how can the Prophet and his family, who were not only martyrs, but whose rank also surpassed that of all other human beings, be considered dead? Calling upon the Prophet and his family does not negate the fact that Allah is the source of help and rescue in this universe. However, because these people are the closest to Him, and they enjoy a special status with Him, then calling upon them means calling upon Allah for the sake of those whom He loves.
 Noble Quran, 28:15
 Ibn Majah; Tirmidhi, al-Nisa’i; “al-Husn al-Hasin” Ibn al-Juzri
 al-Samhudi, Shifa’ al-Asqam
 Noble Quran, 2:45
 Noble Quran, 3:169
 Noble Quran, 2:154