In ordinary poetic expectation, the end of darkness brings relief. Here the speaker makes two apparently opposing statements: alā injalī asks the night to depart; wa-mā al-iṣbāḥu minka bi-amthal then denies that morning is any better.
These are not simply inconsistent assertions. The first voices a natural desire for time to move on, while the second acknowledges the continuing state of inner distress. The result is a contrast between physical daylight and emotional darkness.
The force of the passage comes from the poet qualifying his own plea. The listener discovers that the problem lies deeper than the length of a night: changing the outer landscape need not alter an inner condition.