When one poses a question about one's interpretation of a text, he or she must understand that interpretations are just that, interpretations. Each reader, when examining a text, pulls different ideas, emotions, and understanding from the text in question.
Therefore, as for William Shakespeare's Sonnet 148, one fact that readers can agree on is that it is about love. Five of the poem's fourteen lines contain the word love in them. It is certainly the theme of the poem.
For me, the poem details the problems associated with being in love. According to the sonnet, love is not always beautiful. Instead, love can be blind, full of faults and saddening. That being said, the poem offers a warning to those in love or in search of love.
In the end, Shakespeare is simply offering a warning to people about love. What he seems to want readers to consider is if love is worth the pain it can, and sometimes will, bring.