משך חכמה — וידבר אלהים לישראל במראות הלילה

Q — Why specifically is Yaakov's prophecy described as occurring "בלילה" — both here at the descent to Egypt and earlier in Vayetze?

A — Both moments are thresholds of galut — and the night prophecy teaches "גלו לבבל שכינה עמהם": even in the darkness of exile the Shechinah dwells with Israel; this is why Yaakov instituted Maariv. But that nighttime השראת שכינה is only a CONTINUATION of the daytime presence — Israel keep the Shechinah in galut only if they hold to the mesorah of the Avot, otherwise they are abandoned as a nation that has forgotten its origin.