Why does the speaker in When in disgrace with fortune and mens eyes compare his feelings to those of a lark at break of day when he thinks about his beloved?

The speaker compares his feelings to those of a lark at break of day because, like the lark that sings joyfully at dawn, he finds solace in thinking about his beloved despite his own troubles and lowly position in society. The image of the lark symbolizes hope and beauty in the midst of darkness and despair, reflecting how the speaker's love for his beloved uplifts his spirits.