The harmony of the world is the best testimony to the existence of God
If you consider a watch or a sewing machine or a refrigerator, a motorcycle, a car or an airplane, you will discover a peculiar order in each of them. Do you think it is probable that these precise and neat systems could have arisen on their own and without the involvement of scientists and thinkers?
If you don’t regard this logical that the engine of an airplane with its awesome order and sophistication could have come on its own, then how about the amazing systems operating throughout the world whose every corner is thousand times as exact and precise as the engine of a plane or car. How was it created?
What is the source of the astonishing order and the hidden secrets of the creatures of the world that are so mysterious that they have bewildered the thinkers?
With a little reflection, man’s wisdom and reason will conclude that an Omniscient and Omnipotent Creator has created this orderly world and its manifold creatures.
To appreciate the existence of order in the universe, it suffices to take one part of your body, for instance, your eyes into consideration.
This tiny system, that is, the eye is so precise and sophisticated that even the expert ophthalmologists who have spent years in studying it, are eventually forced to acknowledge their inability to solve all its secrets.
Can any reasonable individual consider it possible that eyes with their astonishing features and their precise structure could have come into existence on their own? The respiratory and digestive systems and other parts of the human body that are created according to special principles and rules do testify to the existence of a wise and capable Creator who has based all these on certain calculations and measurements.
Apart from man and his body, take a seed of wheat or a kernel of almond which emerge from the soil and turn into an ear of wheat or a fruitful tree. Since the seed is planted in the earth and penetrated the soil and emerges from the ground to grow into a shrub or a tree, what extensive and precise systems should be at work until that seed of wheat or that kernel of almond has completed it process. In fact, all these vast and amazing systems like the yearly seasons, days and nights and so on should cooperate like kind nurses so that a shrub or a tree flourishes and we could use their fruits.
Are not the almond tree and the shrub of wheat sufficient evidence to establish the existence of God and His Omnipotence and His Wisdom and Will? Could it be claimed that this order has arisen on its own?
Does man’s reason let him think that sun, moon, stars, seasons, days and nights, and so on, have emerged on their own and does not have any creator? Mufaḍḍal (one of Imām aṣ-Ṣādiq’s disciples) told him, “When we explain the order of the universe, some materialists who are dubious about the existence of God or deny it, say, ‘all these have been created by nature.’”
Imām al-Ṣādiq (‘a) observed,
“If by nature, they mean something that has wisdom, capability and will and freedom, it’s the same as God. They have given it the wrong name (because they have called God, the nature). If by nature, they mean something that does not have power and wisdom, this is out of the question, because it is not possible that such a neat and wonderful world could have been created by a blind and deaf and senseless nature.”
In short, given the conclusions of reason and reflection, the universe possesses a wise and capable Creator who is “God” and it is impossible that an ignorant and senseless nature could have created such a precise system.
 Indirect quotation from Tawḥīd Mufaḍḍal, Najaf, p.55.