John Calvin Commentary Exodus 14:19

"And the angel of God, who went before the camp of Israel, removed and went behind them; and the pillar of cloud removed from before them, and stood behind them:" — Exodus 14:19 (ASV)

And the angel of God. A sudden change that occurred to prevent a battle is described here, for the angel, who used to go before the Israelites to show the way, turned to the other side so that he was placed between the two camps.

This occurred in two respects: the pillar of fire shone upon the Israelites to dispel the darkness of the night, while thick darkness held the Egyptians, as it were, captive, so that they were unable to proceed further. In this way, God both prevented them from advancing and also held out a torch for His people all night to light their way.

He, who had been called "Jehovah" until now, is now designated by Moses as "the Angel." This is not only because angels who represent God often borrow His name, but also because this Leader of the people was God’s only-begotten Son, who was later manifested in the flesh, as I have shown on the authority of Paul (1 Corinthians 10:4). It may also be noted that He is said to have moved here and there, as He showed some sign of His power and assistance.

Furthermore, it appears most clearly that the glory of God, while it enlightens the faithful, on the other hand, overshadows unbelievers with darkness. It is no wonder, then, if nowadays the brightness of the Gospel blinds the reprobate. But we should ask God to enable us to behold His glory.