Word by Word Analysis

وَأَقْسَمُوا۟ بِٱللَّهِ جَهْدَ أَيْمَـٰنِهِمْ لَئِن جَآءَتْهُمْ ءَايَةٌ لَّيُؤْمِنُنَّ بِهَا ۚ قُلْ إِنَّمَا ٱلْـَٔايَـٰتُ عِندَ ٱللَّهِ ۖ وَمَا يُشْعِرُكُمْ أَنَّهَآ إِذَا جَآءَتْ لَا يُؤْمِنُونَ 109

And they swear by Allāh their strongest oaths that if a sign came to them, they would surely believe in it. Say, "The signs are only with [i.e., from] Allāh." And what will make you perceive that even if it [i.e., a sign] came, they would not believe.