Love and difficulty of lovers' separation
The main theme of the poem is that of love. The two lovers are facing a painful farewell and can do nothing about it other than cry. They are fearful because this separation, their being on "diverse shore" means that the love they built will be reduced to nothing. The separation is so painful that the speaker of the poem is afraid that the heaven they built might be dissolved with shared tears. The speaker of the poem asks the lover to not weep so much, because it's too devastating to bear before departing. It is essentially a tragic poem about love and separation.
"Nothing" becomes "all" once a meaning is given to it
The poem portrays another important theme, which is the importance of the meaning of the world around us. In second stanza this is shown as saying that Earth was nothing more than a round ball, before a workman gave names to the places on the map-before meaning was given to the round ball. It was nothing but then it became all. The love between the lovers, the tears they share, once they overflow their heaven, will be reduced to nothing as well. If we go back to the first stanza, the speaker of the poem says that they (the lovers) will become nothing once they are on "a diverse shore", meaning that they are everything to each other now, but once the love dies out due to separation, once it loses its meaning which they gave to it, it will become nothing.
