"If We so willed, We could send down upon them from the sky a sign, so their necks would remain," meaning: so their necks would become, "submissive to it." Mujahid said: This is because they used to ask the Prophet to bring them a sign, so this is a response to their statement.
Muhammad said: "Fathallat" (so they remain) means: their necks will remain; because in the case of a conditional sentence (jazā'), the past tense verb is used to convey the meaning of the future. You say: "In ta'tini akramtuka" (If you come to me, I honored you), which means: "akramuka" (I will honor you).
﴿إِنْ نَشَأْ نُنَزِّلْ عَلَيْهِمْ مِنَ السَّمَاء آيَة فظلت أَعْنَاقهم﴾ يَعْنِي: فَصَارَتَ أَعْنَاقُهُمْ ﴿لَهَا خَاضِعِينَ﴾ قَالَ مُجَاهِدٌ: وَذَلِكَ أَنَّهُمْ كَانُوا يَسْأَلُونَ النَّبِيَّ أَنْ يَأْتِيَهُمْ بِآيَةٍ، فَهَذَا جَوَابٌ لِقَوْلِهِمْ.
قَالَ مُحَمَّدٌ: (فظلت) مَعْنَاهُ: فَتَظَلُّ أَعْنَاقُهُمْ؛ لِأَنَّ الْجَزَاءَ يَقَعُ فِيهِ لَفْظُ الْمَاضِي فِي مَعْنَى الْمُسْتَقْبَلِ؛ تَقُولُ: إِنْ تَأْتِنِي أكرمتك؛ مَعْنَاهُ: أكرمك.
