The Mediation or the Intercession
Quoted from the book (An Hour with Ghosts) By Mohammed-Ali Hassan Al-Hilli

The "mediation" is practiced among created beings, but this act cannot be practiced between God and His servants; because among people there is the noble and the wicked; so that if your need is by the control of a wicked or ignoble man, then he will not grant it you unless you make a mediation or intercession with him.

Whereas the noble or generous man: there is no need for mediation with him; but he will grant you your need without any mediation or intercession. This matter is uncontroversial one.

Then, what do you think about God: isn't He the Most Gracious of all the gracious and the Most Merciful of all the merciful?

God – be glorified – said in the Quran 2: 186
وَإِذَا سَأَلَكَ عِبَادِي عَنِّي فَإِنِّي قَرِيبٌ أُجِيبُ دَعْوَةَ الدَّاعِ إِذَا دَعَانِ
The explanation:
(And when My servants ask you [Mohammed] concerning Me, then, surely, I am Near; I answer the prayer's prayer when he prays to Me.)

Moreover, God – be glorified – said in the Quran 40: 60
وَقَالَ رَبُّكُمُ ادْعُونِي أَسْتَجِبْ لَكُمْ
The explanation:
(And your Lord has said: "Pray to Me and I will hear your prayer.)

So here, God – be glorified – said:
ادْعُونِي أَسْتَجِبْ لَكُمْ
I.e. (Pray to Me, and I will hear your prayer) , but He didn't say: Make an intercession or mediation between Me and you.

In addition, it is mentioned in a prayer of Ali, the son of Hussein – salam be to him:
"Praise be to God on Whom I call whenever I need, and I be in private alone with Him for my secret without any intercessor, and He grants me my need.
Praise be to God on Whom I call and I never call on anyone else; for if I do call on "anyone else", this ["latter"] will not answer my call."

So think and contemplate in this prayer, when he said: "without any intercessor", means: without any mediation, and He grants me my need.

Therefore, learn from it the monotheism and stick to it, and do not seek an intercession with God except your righteous work and your monotheism and devotion to God only; so that you will win and attain Paradise.

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An Hour with Ghosts