What does 'don't judge a book by the cover' mean?

Determine the rhyme scheme of the following poem by elizabeth barrett browning. xxiii is it indeed so? if i lay here dead, wouldst thou miss any life in losing mine? and would the sun for thee more coldly shine because of grave-damps falling round my head? i marvelled, my beloved, when i read thy thought so in the letter. i am thine— but . . so much to thee? can i pour thy wine while my hands tremble? then my soul, instead of dreams of death, resumes life's lower range. then, love me, love! look on me—breathe on me! as brighter ladies do not count it strange, for love, to give up acres and degree, i yield the grave for thy sake, and exchange my near sweet view of heaven, for earth with thee!