And the LORD went before them by day in a pillar of a cloud, to lead them in the way; and by night in a pillar of fire, to give them light; to go by day and night:
All Commentaries on Exodus 13:21 Go To Exodus 13
Augustine of Hippo
Who can doubt that here too God appeared to the eyes of mortal men by a corporeal creature made subject to him and not by his own substance? But it is also not apparent whether it was the Father, or the Son, or the Holy Spirit, or the Trinity itself, the one God. Nor, as far as I can judge, has this distinction been made in that place where it is written: “And the glory of the Lord appeared in the cloud, and the Lord spoke to Moses saying, ‘I have heard the grumbling of the children of Israel.’ ” .