وَقَالُوا۟ لَوْلَا نُزِّلَ عَلَيْهِ ءَايَةٌ مِّن رَّبِّهِۦ ۚ قُلْ إِنَّ ٱللَّهَ قَادِرٌ عَلَىٰٓ أَن يُنَزِّلَ ءَايَةً وَلَٰكِنَّ أَكْثَرَهُمْ لَا يَعْلَمُونَ
10:21; 29:51.
Commentary:
The words, Allah has power to send down a sign, do not mean that though God has the power to send down a sign, yet He will not actually do so. The word قادر (having power) used as active participle is intended to denote readiness to show the required power and the closing words of the verse support that inference.
The word قادر also embodies the sense of measuring and determining (Lane). In this sense, the clause would mean that God is devising means for the success of Islam, for people are already joining Islam and swelling the number of Muslims. This is a clear indication of the will of God, but disbelievers would not ponder over it. The Quran makes this point clear by suitable illustrations in the following verse.
10:21; 29:51.