فَلَمَّا تَرَاءى الْجَمْعَانِAnd when the two hosts saw each other,means, each group saw the other.At that point,قَالَ أَصْحَابُ مُوسَى إِنَّا لَمُدْرَكُونَthe companions of Musa said:"We are sure to be overtaken."This was because Fir`awn and his people caught up with them on the shores of the Red Sea, so the sea was ahead of them and Fir`awn and his troops were behind them. Hence they said:إِنَّا لَمُدْرَكُونَ (We are sure to be overtaken).قَالَ كَلَّ إِنَّ مَعِيَ رَبِّي سَيَهْدِينِ