Reply: From the viewpoint of reason and logic of revelation, just as all human beings, nay, all phenomena of the world, are in need of God in their creation, they are also in need of Him for their subsistence.
In this regard, the Holy Qur’an states:

“O mankind! You are the ones who stand in need of Allah, and Allah - He is the All-sufficient, the All-laudable.”
In another place, it attributes all victories to the Lord of the worlds, stating:

“And victory comes only from Allah, the All-mighty, the All-wise.”
Abiding by this principle confirmed by Islam, we, Muslims, recite this noble verse in every prayer:

إِيَّاكَ نَعْبُدُ وَإِيَّاكَ نَستَعِينُ

“You {alone} do we worship, and to You {alone} do we turn for help.”
Now, let us clarify the abovementioned question:
Seeking help from someone other than God is viewed in two ways:
1. The first is that we seek assistance from another man or phenomenon by holding that he or it is independent in his or its power or action, and supposing him or it as needless of God in giving assistance.
Without any doubt, seeking assistance from someone other than God in this way is sheer polytheism. The Holy Qur’an points to its futility in the following verse:

“Say, ‘Who is it that can protect you from Allah should He desire to cause you ill, or desire to grant you mercy?’ They will not find for themselves any protector or helper besides Allah.”
2. The second is that we seek help from another person by holding that that person is someone who is in need of God, as not independent and that his power comes from God, the Exalted, through which to solve some of the problems of the servants (of God).
On the basis of this mindset, the one from whom we seek is granted “mediation” by God, the Exalted, for fulfilling some of the needs. Seeking help in this way is, in reality, seeking assistance from God Who has endowed existence to these mediums and intermediaries, and granted power and effect to them for fulfilling others’ needs. In principle, the life of every human being is founded on seeking help from mediums and intermediaries without which man’s life will be chaotic.
Now, if we look at these mediums as the agents for fulfilling the assistance of God and hold that they have been originated and granted power by Him, in this case seeking help will by no means contradict monotheism.
If a devoted godly farmer seeks aid through such agents like land, water, air, and the sun to plant seeds and bring them up until they yield fruit, he has actually sought help from God because it is He Who has given power and activity to these agents.
It is clear that seeking assistance in the mentioned way is totally consistent with the spirit of monotheism. In fact, the Glorious Qur’an invites us to seek assistance through such things like patience and prayer as in the following verse:

“And take recourse in patience and prayer.”
It is evident that constancy and patience is a human attribute, yet we are invited to seek assistance through it. The aforementioned way of seeking assistance is not inconsistent with turning for help to God as stated in the following verse:
“You {alone} do we worship, and to You {alone} do we turn for help.”

Is calling on someone tantamount to worshipping him and to polytheism?
What has prompted this question to be posed is the outward meaning of some of the verses of the Qur’an, which seemingly prohibit invoking anyone other than Allah.
“The places of worship belong to Allah, so do not invoke anyone along with Allah.”
“Nor invoke besides Allah that which neither benefits you nor can do you any harm.”
Referring to such verses, a group of people hold that calling on others and invoking dead sacred figures or righteous people as polytheism and an act of worshipping them.
Reply: In order to make clear the answer to this question, we ought to explain the meaning of the two terms, du‘a’ {supplication} and ‘ibadah {worship}: As a matter of fact, the word “du‘a” literally means “calling” and “invoking” while the term “‘ibadah” means “worship”, and these two terms should not be considered synonymous. That is, the word “call” or “invocation” does not always mean “worship” for the reasons that follow:
First: The term “da‘wah” (a derivative of du‘a’) has been used in some Qur’anic verses but not in the sense of “‘ibadah”. For example:
“He (Nuh) said, ‘My Lord! Indeed I have summoned my people night and day’.”
Can we say that what Nuh (Noah) (‘a) meant is: “I have worshipped my people night and day”?
As such, it cannot be said that da‘wah and ‘ibadah are synonyms, or that to seek help from the Prophet or a righteous person is to worship him; for, da‘wah or nida’ {call} has more general meaning than worship.
Second: Du‘a’ in these verses does not absolutely mean invocation; rather, it means a particular call which can be a constituent part of the word “worship”; for, this group of verses are about idol-worshippers who took their idols as gods.
No doubt idol-worshippers’s humility, supplication and imploration were dedicated to the idols they described as possessors of the right of intercession, forgiveness, etc. and recognized as independent possessors of the affairs in this world and the hereafter. It is obvious that under such conditions to turn to these creatures in supplication or request of any kind will be considered as worship and devotion.
As vivid evidence to the fact that the idol-worshippers’ supplication or invocation is an expression of their belief in the divinity of idols, we introduce the following verse:
“Of no avail to them were their gods whom they would invoke besides Allah, in any wise.”
Therefore, the verses under discussion are irrelevant to our subject; our subject is concerned with the asking of one servant from another servant (of God) whom the former does not regard as lord and god nor an omnipotent master and possessor of the affairs in this world and the hereafter; rather, he regards him as an honorable servant who is loved by God and has been chosen for the station of prophethood or imamah {leadership} and God has promised to grant his supplication on behalf of His servants as He says:
“Had they, when they wronged themselves, come to you and pleaded Allah for forgiveness, and the Apostle had pleaded for forgiveness for them, they would have surely found Allah all-clement, all-merciful.”
Third: The quoted verses prove clearly that calling on someone {da‘wah} does not mean mere asking for a need or something to be done but a ‘devotional’ call. As such, in one of the verses, the term “‘ibadah” has been mentioned immediately after the word da‘wah:
“Your Lord has said, ‘Call Me, and I will hear you{r supplications}!’ Indeed those who are disdainful of My worship will enter hell in utter humility.”
We notice that at the beginning of the verse, the term “ud‘uni” {call me} is followed by the term “‘ibadati” {My worship}. This testifies to the fact that da‘wah means a particular way of asking or seeking help from certain beings that have been recognized as having divine attributes.

Conclusion
From the three stated preliminaries, we reach the conclusion that the main purport of these Qur’anic verses is prohibition from calling upon the groups of idolaters who regard the idols as partners of God or having the power of intercession, and from any gesture of humility, meekness, or lamentation, seeking assistance, pleading, and request for intercession, or seeking help for the fulfillment of need with the belief that they are gods who have been commissioned to do divine acts and to do some acts related to this world and the hereafter.
What relationship do these verses have with imploring a pure soul which, according to the supplicator has not gone a speck beyond the limit of servitude, but a beloved and honorable servant of God?!
When the Qur’an says:
“The places of worship belong to Allah, so do not invoke anyone along with Allah,”
it refers to the way the Arabs before Islam called upon the idols, celestial bodies, angels, and jinns that they worshipped. This verse and other related verses are pertaining to calling upon a person or thing deemed as an object of worship.
No doubt, requesting from these beings in such a belief is tantamount to worshipping them. But what do these verses have to do with the idea of asking a person to pray for you without considering that person as god, lord or capable of governing world, but treats him instead as a worthy servant whom God loves?
Some may imagine that one can call on outstanding godly figures only when they are alive and it is an act of polytheism to do so after their demise. In reply, we say:
First: It is from the pure souls of such good servants (of God) as the Prophet and the Imams (‘a) who are, as described by the Qur’anic verses, alive and leading their purgatorial {barzakhi} life, that we seek aid and not from their dead bodies in the ground. And our presence in the vicinity of their shrines contributes to strengthening our communion with and attention to their sacred souls. According to hadiths, in these sites supplications are granted.
Second: Their being alive or dead cannot be a criterion for distinguishing monotheism from polytheism. It is worth noticing that our discussion is about the criteria of polytheism and monotheism, and not about the importance or unimportance of these supplications.
Of course, this issue (that is, the importance or unimportance of this kind of implorations) has been treated elsewhere.