The Barrier restrains Them, but It will be breached when the Hour draws nigh

Allah tells us that Ya'juj and Ma'juj could not climb over the barrier or penetrate its lower portion. Varying forms of the verb are used here in the Arabic text to reflect the difficulty of the action referred to.

فَمَا اسْطَـعُواْ أَن يَظْهَرُوهُ وَمَا اسْتَطَـعُواْ لَهُ نَقْبًا

Commentary

As for the pronoun of the word: بَعْضَهُمْ (ba` dahum) in بَعْضَهُمْ يَوْمَئِذٍ يَمُوجُ فِي بَعْضٍ (And on that day, We will leave them [ Ya’ juj and Ma'juj ] surging over one another - 99), it is obvious that it reverts back to Ya'juj Ma juj. Then, as for their condition described therein - 'surging over one another' - it is also obvious that this will be their state when the passage lies open for them and they will be hastening their way from the hilly heights down to the ground. Commentators have suggested other probabilities as well.