يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ ٱتَّقُوا۟ ٱللَّهَ وَءَامِنُوا۟ بِرَسُولِهِۦ يُؤْتِكُمْ كِفْلَيْنِ مِن رَّحْمَتِهِۦ وَيَجْعَل لَّكُمْ نُورًا تَمْشُونَ بِهِۦ وَيَغْفِرْ لَكُمْ ۚ وَٱللَّهُ غَفُورٌ رَّحِيمٌ
Yaaa ayyuhal lazeena aamaanut taqullaaha wa aaminoo bi Rasoolihee yu'tikum kiflaini mir rahmatihee wa yaj'al lakum nooran tamshoona bihee wa yaghfir lakum; wallaahu Ghafoorur Raheem
You who believe, be mindful of God and believe in his Messenger; he will give you a double share of his mercy, and grant you a light by which you walk, and forgive you. God is forgiving, merciful.
Believers are told to believe, and the tradition read that doubling in two ways. Coming straight after the followers of Isa, the address was taken by many commentators as meant for those among them who had faith and were now asked to accept Muhammad too, making kiflayn, the two portions, one for each; others heard a call to Muslims to hold firm. The verse after names the People of the Book outright, and 28:54 promises some of them a reward twice over.