As noted earlier, this is the main goal of Islam. It is also one of its excellent features. Islam frees the human from trying to serve varied objects of worship. His life becomes clear and easy to follow. He has one Lord and one path to follow. He does not associate anyone or anything with God.
In a number of places in the Quran, Allah juxtaposes the ramifications and effects of the correct belief in Allah with the effects of different incorrect beliefs. In the following passage, Allah has beautifully described the fruits of the correct belief as well as the results of all false beliefs.
Don’t you see how Allah sets forth a parable? A goodly word is like a goodly tree, whose root is firmly fixed, and its branches (reach) to the heavens, it brings forth its fruit at all times, by the leave of its Lord. So Allah sets forth parables for men, in order that they may receive admonition. And the parable of an evil word is that of any evil tree. It is torn up by the root from the surface of the earth. It has no stability. Allah will establish in strength those who believe, with the word that stands firm, in this world and in the Hereafter; but Allah will leave to stray those who do wrong. Allah does what He wills
It is narrated that ibn Abbaas said
The goodly word is the testimony that there is none worthy of worship except Allah
Quoted in ibn Katheer, Tafseer (Daar Taibah), vol. 4, p. 491
This verse shows that pure monotheism or proper belief is the foundation upon which all other good is built. It is a foundation that continues to give and give, with its proceeds reaching the highest limits. Such is the way with the true faith; it continually and perpetually benefits the person in this life and eternally in the Hereafter. It also follows that the stronger and better supported the foundation or roots, the greater will be the fruits. On the other hand, the false beliefs, such as associating partners with God, have no solid ground to them. Indeed, they are not much more than an illusion in the sense that they can never bear the produce that its followers claim or believe in.
It is therefore no secret and no wonder that the first portion of the Prophet’s mission, as demonstrated by the revelations that he received in Makkah, concentrated on purification of belief. It was dedicated to removing all forms of ignorance, superstition and false creeds, as a human’s soul cannot rest if it is torn in many directions, seeking after numerous ultimate goals.
Allah has beautifully described the similitude of those who fail to see that their soul can only recognize one true object of worship:
Allah puts forth a similitude: a [slave] man belong to many partners disputing with one another [like those who worship more than one god] and a [slave] man belonging to only one man [like those who worship only Allah]. Are those two equal in comparison? All the praises are to Allah. Yet most of them know not
From an Islamic perspective, there is no way for a person to please more than one god as, by the Islamic definition of the word “God”, God must be the thing that is foremost in one’s heart.
Actually, when a person realizes that he has only one, clear goal, the effects upon his soul are profound. He need not chase after an endless array of goals, never being able to satisfy or achieve any of them completely. (Indeed, many times people’s goals are contradictory and they can never achieve all of them.) His energies need not be exhausted trying to serve a myriad of goals. When he has one goal and one goal alone, he can easily gauge whether he is moving towards achieving that goal or not. He can put all of his energy and thought into working towards that one ultimate goal. He can be certain about his goal and his path will be clear. Hence, he has no reason to be filled with doubt or confusion.
Then, as he moves closer and closer to that one ultimate goal, he can experience true joy and contentment. All of this is part of the beauty and the bounty when humans recognize, receive and accept true monotheism, the only faith system consistent with their own creation and nature.