Allah said;
(So the Sayhah overtook them) This is the piercing sound that came to them when the sun rose, which was accompanied by the city being flipped upside down, and stones of baked clay (As-Sijjil) raining down upon them. The discussion of As-Sijjil in Surah Hud is a sufficient explanation. Allah said:
(Surely, in this are signs for those who see.) meaning that the traces of the destruction of that city are easily visible to any one who ponder about it, whether they look at it with physical eyesight or mental and spiritual insight, as Mujahid said concerning the phrase,
(those who see) he said, "those who have insight and discernment." It was reported from Ibn `Abbas and Ad-Dahhak that it referred to those who look. Qatadah said: "those who learn lessons".
(those who see) therefore the meaning is "those who ponder".
(And verily, they were right on the highroad.) meaning that the city of Sodom, which was physically and spiritually turned upside down, and pelted with stones until it became a foul smelling lake (the Dead Sea), is on a route that is easily accessible until the present day. This is like the Ayah,
(Verily, you pass by them in the morning, and at night. Will you not then reflect) (37:137-138).
(Surely, there is indeed a sign in that for the believers.) meaning, `All that We did to the people of Lut, from the destruction and the vengeance, to how We saved Lut and his family, these are clear signs to those who believe in Allah and His Messengers.'