Rashi on Exodus 14:19/רש"י על שמות י״ד:י״ט

1וילך מאחריהם AND WENT BEHIND THEM to divide the camp of Egypt from the camp of Israel and to receive the arrows and the missiles of the Egyptians. Everywhere it says “The Angel of the Lord (ה׳)” whilst here we have The Angel of God (אלהים).”! The name אלהים really denotes, wherever it occurs, “Judge” (lit., “judgment”). Therefore the use of this term here teaches us that Israel was, at that moment, arraigned in judgment, whether to be saved or to be destroyed together with Egypt (Mekhilta).

2ויסע עמוד הענן AND THE PILLAR OF CLOUD WENT [FROM BEFORE THEM] — When it became dark and the pillar of cloud handed over the camp to the pillar of fire, the cloud did not go away as it was accustomed to go away altogether in the evening, but it went and betook itself behind them to make it dark for the Egyptians.