Wakathalika zayyana likatheerin mina almushrikeena qatla awladihim shurakaohum liyurdoohum waliyalbisoo AAalayhim deenahum (surah Anam: 137)

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

(6:137) And, likewise, the beings supposed to have a share in Allah's divinity have made the slaying of their offspring seem lawful to many of those who associate others with Allah in His divinity *107 so that they may ruin them *108 and confound them regarding their faith. *109 If Allah had so willed, they would not have done that. Leave them alone to persist in their fabrication.  *110

Wa kazaalika zaiyana likaseerim minal mushrikeena qatla awlaadihim shurakaaa`uhum liyurdoohum wa liyalbisoo `alaihim deenahum wa law shaaa`al laahu maa fa`aloohu fazarhum wa maa yaftaroon

*107). The word 'partners' is now used in a different sense. In this verse the word 'partners' denotes those human beings and devils who had legitimized infanticide and even represented it as a commendable act.
The reason for calling such people 'partners' is that just as God alone deserves to be worshipped, so He alone has the right to make laws for His creatures and to determine the limits of what is lawful and what is unlawful. Also, just as consecrating acts of devotion to anyone other than God amounts to setting up partners with Him, so to follow man-made laws in the belief that human beings have the right to be their own law-makers amounts to acknowledging others as partners of God. Both these acts amount to setting up partners with Him, irrespective of whether or not man applies the word 'God' to those before whom he makes ritual offerings, or to those whose laws he considers to be essentially right and binding for men.
It is pertinent to recall that three forms of infanticide were practised among the Arabs, and the Qur'an alludes to each:
(1) Girls were put to death either to forestall the intrusion of a son-in-law, to prevent them from falling into the hands of enemies in the event of an outbreak of tribal feuding or to stop them from becoming a source of disgrace for any other reason.
(2) Both male and female children were killed if parents thought they would not be able to support them and that they would thus become an unendurable burden.
(3) Children of both sexes were placed as sacrificial offerings on the altars of the deities in order to gratify them.
*108). The use of the word 'ruin' in this verse is significant. It denotes, in the first place, the moral ruination of a people. A man whose callousness and cruelty reach the point where he begins to kill his offspring with his own hands not only becomes bereft of the essence of humanity, but has sunk even lower than the animals. Moreover, this signifies the ruin of a people and of the human race. This is because infanticide necessarily leads to loss of population which is detrimental to the interests of mankind and also of each nation, since it prevents those who could have carried the legacy of a nation from either being born or puts an end to their lives after ,they are born. This rule also signifies the ultimate ruin, i.e. in the Hereafter. For indeed anyone who treats innocent children with such high-handedness, who cold-bloodedly slaughters the essence of his humanity, who acts so sordidly towards the human species as such, and even towards his own people, deserves severe punishment from God.
*109). In the Jahiliyah, the Age of Ignorance, the Arabs both identified themselves with Abraham and Ishmael and were quite convinced that they were indeed followers of Abraham and Ishmael. They therefore considered their religion to be one that had been prescribed by God. The fact, however, was that over the course of centuries a number of innovations had overgrown the religion preached by Abraham and Ishmael. These innovations, which had been introduced by their religious leaders, the tribal chiefs and the elders of noted families, had become hallowed with the passage of time, and were considered an integral part of their original religion. No authentic traces of this original religion, however, existed in the Arab traditions, nor in written sources nor in historical records as such. Hence, when innovations made their inroads into their religious life, they failed to perceive both the innovations and the innovators. This rendered the entire religious tradition of the Arabs unauthentic in the sight of the people of Arabia themselves. They could not assert with conviction which elements were part of the original God-given religion, and which were mere innovations.
*110). Had God not so willed, they could never have kept to their false ways. But God willed that everybody should be allowed to pursue his own choice. Hence, if people do not believe in spite of the Prophet's admonition, and persist in their false ways, they must be allowed to do as they please. One need not hound such people and pester them into accepting the Truth.