'Tranquil' in the poem refers to the state of mind the narrator is in as he thinks about how the the person he is loves and how he can be with them by overcoming his mistakes and showing her he can be the man of her dreams.
'Tranquil' in the poem refers to the state of mind the narrator is in as he thinks about how the the person he is loves and how he can be with them by overcoming his mistakes and showing her he can be the man of her dreams.