And indeed We saved the Children of Israel from the humiliating torment from Fir`awn; verily, he was arrogant and was of the excessive.
Here Allah reminds them of how He saved them from their humiliation and subjugation at the hands of Fir`awn, when they were forced to do menial tasks.
إِنَّهُ كَانَ عَالِيًا مِّنَ الْمُسْرِفِينَ
(verily, he was arrogant),
means, he was proud and stubborn.
This is like the Ayah:
إِنَّ فِرْعَوْنَ عَلَ فِى الاٌّرْضِ
Verily, Fir`awn exalted himself in the land, (28:4)
فَاسْتَكْبَرُواْ وَكَانُواْ قَوْماً عَـلِينَ
but they behaved insolently and they were people self-exalting, (23:46)
He was one of the excessive and held a foolish opinion of himself.
وَلَقَدِ اخْتَرْنَاهُمْ عَلَى عِلْمٍ عَلَى الْعَالَمِينَ