أَفَلَمْ يَسِيرُوا فِي الاَْرْضِHave they not traveled through the land,means, have they not traveled in the physical sense and also used their minds to ponder!That is sufficient, as Ibn Abi Ad-Dunya said in his book At-Tafakkur wal-I`tibar,"Some of the wise people said, `Give life to your heart with lessons, illuminate it with thought, kill it with asceticism, strengthen it with certain faith, remind it of its mortality, make it aware of the calamities of this world, warn it of the disasters that life may bring, show it how things may suddenly change with the passing of days, tell it the stories of the people of the past, and remind it what happened to those who came before."' Walk through their ruins, see what they did and what became of them, meaning, look at the punishments and divine wrath that struck the nations of the past who belied,فَتَكُونَ لَهُمْ قُلُوبٌ يَعْقِلُونَ بِهَا أَوْ اذَانٌ يَسْمَعُونَ بِهَاand have they hearts wherewith to understand and ears wherewith to hear,meaning, let them learn a lesson from that.فَإِنَّهَا لَاإ تَعْمَى الاْإَبْصَارُ وَلَكِن تَعْمَى الْقُلُوبُ الَّتِي فِي الصُّدُورِVerily, it is not the eyes that grow blind, but it is the hearts which are in the breasts that grow blind.means, the blind person is not the one whose eyes cannot see, but rather the one who has no insight. Even if the physical eyes are sound, they still cannot learn the lesson