Wallatheena kaththaboo bi-ayatina summun wabukmun fee aththulumati man yasha-i Allahu yudlilhu waman (surah Anam: 39)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(6:39) Those who gave the lie to Our signs are deaf and dumb and blunder about in darkness. *27 Allah causes whomsoever He wills to stray in error, and sets whomsoever He wills on the straight way.'  *28

Wallazeena kazzaboo bi Aayaatinaa summunw wa bukmun fiz zulumaat; mai yasha il laahu yudlilh; wa mai yashaa yaj`alhu `alaa Siraatim Mustaqeem

*27). If they are concerned with miraculous signs in order to determine whether or not the message of the Prophet (peace be on him) is indeed true, then, let them look around with open and attentive eyes. If they actually do so they will find the world full of such signs. Let them take any species of animal or bird they like. They can reflect upon the superbness of its organic structure. They will notice how its instinctive urges are in complete conformity with its natural requirements. They will also observe how wonderfully adequate are the arrangements for providing it with nourishment; how marvellously well-determined are the limits within which -it lives; how tremendously efficient is the system under which each living creature is protected, provided for, looked after and directed towards self-fulfilment; how strictly each one is fitted into the framework of the discipline devised for it, and how very smooth is the operation of the whole system of birth, procreation and death. Were one to reflect on this alone from among the innumerable signs of God, one would perceive fully how true the teaching of the Prophet (peace he on him) is concerning the unity and other attributes of God and how necessary it is to live a righteous life in conformity with the concept of God propounded by him. But their eyes were neither open to perceive the Truth nor their ears open to heed admonition. Instead, they remained ignorant, preferring to be entertained by the performance of wondrous feats.
*28). God's act of misguiding a man consists in not enabling one who cherishes his ignorance to observe the signs of God. The fact is that if a biased person - one who has no real love of the Truth - were to observe the signs of God, he might still fail to perceive it. Indeed, all those things which cause misconception and confusion would probably continue to alienate him from it. God's act of true guidance consists in enabling a seeker after the Truth to benefit from the sources of true knowledge, so that he constantly discovers sign after sign, leading him ultimately to the Truth.
A myriad of cases are encountered daily to illustrate this. We notice that a great many people pass inattentively over the countless signs of God that are scattered all over the world, and ignore even those signs which are manifest in human beings as well as in animals. It is little wonder, then, that they derive no lesson from all these signs. There are many who study zoology, botany, biology, geology, astronomy, physiology, anatomy and other branches of natural science. Others study history, archaeology and sociology. During the course of such studies they come across many signs of God which, if they cared to look at them in the correct perspective, might fill their hearts with faith. But since they commence their study with a bias, and are actuated only by the desire to acquire earthly advantages, they fail to discover the signs which could lead them to the Truth. On the contrary, each of those very signs of God contributes to pushing them towards atheism, materialism and naturalism. At the same time, the world is not empty of those truly wise ones who view the universe with open eyes. For them even the most ordinary phenomenon of the universe directs them to God.