Whom does God let go astray and seal on the heart?

 

Verses 34-35 of Chapter 40:
Before this Joseph had brought to you clear Signs, but you continued to be in doubt concerning his teachings. Then, when he died, you said, "Allah will never send another Messenger after him." Likewise, Allah lets go astray the transgressors and doubters who dispute concerning the Revelations of Allah even without any authority having come to them. Such an attitude is abhorred by Allah and the believers. Thus does Allah set a seal on the heart of every arrogant, self-exalting person.

 
Verses 23-24 of Chapter 45:
Then seest thou such a one as takes as his god his own vain desire? Allah has, knowing (him as such), left him astray, and sealed his hearing and his heart (and understanding), and put a cover on his sight. Who, then, will guide him after Allah (has withdrawn Guidance)? Will ye not then receive admonition? And they say: “What is there but our life in this world? We shall die and we live, and nothing but time can destroy us.” But of that they have no knowledge: they merely conjecture.