"This is [a set of] insights for mankind," meaning: the Quran, "and a guidance" by which they are guided, "and a mercy for a people who are certain [in faith]."
Muhammad said: The singular of 'basa'ir' (insights) is 'basirah'.
﴿هَذَا بصائر للنَّاس﴾ يَعْنِي: الْقُرْآن ﴿وَهدى﴾ يَهْتَدُونَ بِهِ ﴿وَرَحْمَةٌ لِقَوْمٍ يُوقِنُونَ﴾.
قَالَ مُحَمَّدٌ: وَاحِدُ الْبَصَائِرِ: بَصِيرَةٌ.