The speaker states that ever since their eyes became accustomed to the night, the night has been the sole cause of their wakefulness.

This beautiful couplet speaks to the profound nature of emotional awakening. The poet suggests that the moment his eyes became accustomed to the darkness of night, the night itself became the catalyst for his consciousness. It's not just about seeing; it's about being emotionally stirred by the silence and the hours when the world sleeps. It captures that feeling of inescapable introspection that only the late hours bring.