Reason is the gift with which we should form firm belief. To form a false belief is a Shirk, a term that means ‘mixing’ in the sense of mixing truth and falsehood which results in confusion, metaphorically this mixing will make you drown when released from the training pool, into the ocean of true reality, so your shepherds are a vital aspect of this life.
A wrong belief does nothing to the Creator, but it is devastating to the individual holding on to this sinking stone. So a Shirk acts like a sinking stone, it pulls you down, and only the divine spark of reason can make you unchain yourself from this burdensome stone.
The ocean of deep reality we dive into, has absolute purity of truth, outside of humanities energy form, not a single lie exists within its infinite knowledge.
So the acceptance of falsehood, from any, and all religion, all equally worthless, or from social indoctrinations, or from historical family beliefs pasted down without investigation, makes you a non-believer in truth, and these shirks (mixture of truths and falsehoods), or false shepherds will spell your ultimate misery.
Shirk / Mushrik / Mushrikeen
Ash-Shirko is to get mixed up, to remain stuck (Qamoos al-Moheet).
Shirk is a special term used by the Quran, which means:
The concept is that as all human beings are created equal, no one is superior to someone else in his capacity as a human being, and therefore, no one has the right to rule anyone else. Moreover, since everything existing in the universe has been subjugated to Man, there is nothing superior to him, with one exception: Allah. To consider someone superior to man, therefore, amounts to degrading one's own self, and also putting that entity at par with Allah. This is Shirk. It makes no difference to Allah, but only to man, as he falls from his superior position. The Quran, therefore, considers Shirk as the biggest crime against man as it takes away his rightful position from him (31/13).
Obedience of just one authority, that is Allah, through his revealed Book, and command and control over the entire universe is Tauheed (Unity of Allah, monotheism), the slightest deviation from being Shirk.
At the time of emergence of Islam, there were two categories of people. The first were those who claimed to be the followers of previous Rusul, like Jews or Christians, whom the Quran called Ahl-ul-Kitab. The other category was those who neither claimed nor obeyed any Divine Book, but followed their own codes or other man-made laws. Some of them also recognised Allah but along with Him, also acknowledged other forces or powers. They were called Mushrikeen. But since both the categories did not accept the Quran, they were together called Kafireen.
In actual life, whether a person belongs to Ahl-ul-Kit'ab (Jews, Christian, etc.) or not, if he obeys laws made by man, according to the Quran he is a Mushrik, however pious or saintly he may be. Deen and Tauheed is a straight path. Various factions and sects are the diversions which take him away from this path, and if he travels long enough on these diversions, the true path gets eventually lost. The Quran has, therefore, termed sectarianism as Shirk (30/31-32). Every sect leads to and ends up with some person as the last authority, whereas in Deen the final authority is only the Holy Quran.
As commonly believed, the worship of idols or dead persons is not the only aspect of Shirk; the greatest Shirk is to equate man-made laws with the Laws of Allah. The Quran says that such people consider themselves Momineen, whereas in actual fact they are Mushrikeen (12/106).
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