Alā calls for attention. Ayyuhā forms a vocative expression, followed by al-layl al-ṭawīl, the identified addressee. An inanimate night is made capable of being addressed in the language of an intimate plea.
Injalī belongs to the root family j-l-w / j-l-y (ج ل و / ج ل ي), with the sense of becoming clear or dispersing. Here it is a request or command that the night disappear, not an actual order to a human listener.
In mā ... bi-amthal, mā is negative, and the bāʾ with the predicate reinforces negation. Amthal conveys the comparative idea of being better or more favorable.