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Seest thou not?-i.e. with thy mental vision. The incident happened in the very year of the holy Prophet's birth, barely two months before it.
These were the troops of Abraha the Abyssinian, who invaded Makkah with a large army, in which were some elephants. See Introduction to this Sura.
The miracle consisted in the birds coming in large flights and flinging stones at the army which destroyed the whole of Abraha's army.
Sijjil: see n. 1579 to xi. 82. The word also occurs at xv. 74. Stones of baked clay, or hard as baked clay, are part of the miracle in the story.
A field, from which all the corn has been eaten up and only straw with stalks or stubble is left, is a field dead and useless. And such was the army of Abraha,-dead and useless. Another possible rendering would be: "like eaten straw and stubble found in the dung of animals". The meaning would be the same, but much more emphatic.
The lesson to be drawn is twofold. For the Pagan Quraish of Makkah it was: Allah will protect His own; if you persecute the holy Prophet, he is greater than the mere building of the Ka'ba: will not Allah protect him? For men in all ages it is: 'a man intoxicated with power can prepare armies and material resources against Allah's holy Plan; but such a man's plan will be his own undoing; he cannot prevail against Allah'.