John Gill Commentary Nehemiah 9:17

"and refused to obey, neither were mindful of thy wonders that thou didst among them, but hardened their neck, and in their rebellion appointed a captain to return to their bondage. But thou art a God ready to pardon, gracious and merciful, slow to anger, and abundant in lovingkindness, and forsookest them not." — Nehemiah 9:17 (ASV)

And refused to obey
Though exhorted, admonished, and threatened, such was their obstinacy:

neither were mindful of your wonders that you did among them ;
in delivering them at the Red sea, in raining manna about them, and giving them water out of the rock:

but hardened their necks ;
see the preceding verse:

and in their rebellion appointed a captain to return to their bondage ;
they not only proposed it, but determined upon it, which is reckoned the same as if they had done it, see (Numbers 14:4) ,

but you are a God ready to pardon, gracious and merciful, slow to
anger, and of great kindness ;
as he had proclaimed his name before Moses, and as the whole of his conduct towards the people of Israel abundantly shewed, see (Exodus 34:6Exodus 34:7)

and forsookest them not ;
when in the wilderness, where otherwise they must have perished, but still fed and protected them, notwithstanding their provocations.