6. "There is an infirmity in their hearts and God hath increased that infirmity." (Surah 2: 9.)
C. ~ Well did God increase their infirmity, while they were innocent? Did He not have pity on them? They must have suffered terribly indeed. Is not this act more devilish than that of the Devil? To seal their hearts and increase their infirmity could never be the work of God inasmuch as the increase of infirmity is the result of one's own sinful actions.
Rejecting the truth after it becomes manifest is a crime before God Almighty. Now, the meaning of this verse is that when a person does so and refuses to accept the truth, he is himself responsible for closing his eyes and ears as per the eternal law of God. This is a punishment from God given to those who deny the truth (Arabic. Allazeena Kafaroo). It is not a punishment to the innocents as you have falsely alleged. To understand this let us see what Swamiji himself says in Satyarth Prakash.
"Though the human souls posses the capacity for ascertaining truth, yet through self-interest, obstinacy, wrong-headedness, ignorance and the like, it is led to renounce truth and incline towards untruth.” [English Satyarth Prakash Introduction, P ii, ]
“What a wonderful progress have they (i.e., the Buddhists) made in ignorance? They have really no equal in this respect. It is certain that this is the result of their opposing the Veda and God.” [English Satyarth Prakash, Chapter 12, Page 518]
Notice that Swamiji considers the increase in the ignorance of Buddhists the consequence of their opposing the Veda and God. Similarly, as a consequence of rejecting the truth of Islam after it has become manifest, people sink in ignorance, which is compared to the sealing of the hearts.
Listen also to what Yajur Veda Adhyay 25; Mantra 13 says,
“… Ishwar who bestows knowledge and disobedience of His Will is death…”
Let me give you another example to make you understand. A Judge punishes a criminal by imprisoning him, thus limiting his freedom to see and hear as a normal free person. Actually the criminal deserved to be punished and his imprisonment is the consequence of what he did, but because the Judge pronounced the verdict, we say that the Judge imprisoned him.
Concerning increasing the infirmity; this also is as per the laws of God Almighty. If a patient refuses to abstain from the food which is harmful for his health, his infirmity is bound to increase as per the law of nature.Same is the case with spiritual infirmity.