John Gill Commentary Nehemiah 9:19

"yet thou in thy manifold mercies forsookest them not in the wilderness: the pillar of cloud departed not from over them by day, to lead them in the way; neither the pillar of fire by night, to show them light, and the way wherein they should go." — Nehemiah 9:19 (ASV)

Yet you in your manifold mercies did not forsake them in the wilderness Where no supply could be had, if he had cast them off, see (Nehemiah 9:17) ,

the pillar of the cloud did not depart from them by day, to lead them in the way ; which, if it had, they would have been scorched by the heat of the sun:

neither the pillar of fire by night, to show them light, and the way in which they should go ; or otherwise they would have lost their way, and not have known which way to have gone.