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Then did they not travel in the earth so as to have hearts (minds) with which they could understand or ears with which they could hear? Then certainly, the eyes are not blind but the hearts, that are in the bosoms, are blind. (Al Quran, Surah Al Haj, Chapter 22: Verse 46)
The above verse shall be read in context with the following verses:
22-42: And if they deny you, then before them, the people of Nuh and Aad and Samood had also denied,
22-43: along with the people of Ibrahim and people of Lut
22-44: and the inhabitants of Midian. And Musa was also denied; so I gave to the infidels time (for amending themselves) then caught them. Then how was My rejection (of them)?
22-45: So how many a town did We destroy while it was unjust, so it fell down on its roofs with (many a) deserted well and lofty palace reduced in size.
22-46: Then did they not travel in the earth so as to have hearts (minds) with which they could understand or ears with which they could hear? Then certainly, the eyes are not blind but the hearts, that are in the bosoms, are blind.
Summarized Commentary:
Messengers who had come before Prophet Muhammed (PBH) were also denied and those who rejected were destroyed. Even after seeing this they deny, which shows that their hearts / minds are blind i.e. religious information is filtered out from their receptive powers therefore there is no religious response.
On the other hand Quran is inviting human beings to reflect, when they travel around the world and see old abandoned forts, palaces, relics of ruined cities and places of natural calamities, etc. and question and ponder why they were destroyed? The reason for their destruction is given in these verses.