Shall I give you white currants?
I do not know why, but I have a sudden fancy for this fruit.
At the moment, the idea of them cherishes my senses,
And they seem more desirable than flawless emeralds.
Since I am, in fact, empty-handed,
I might have chosen gems out of India,
Very often, especially in biblical literature, fruit symbolizes virginity, temptation and pleasure.  Although aware of her desire for this fruit, the speaker doesn’t yet understand why she has this desire.  The fruit could be someone she wishes to be with or, just in general, something she is tempted by. 
 By saying “at the moment”, the speaker is implying that this is just crossing her mind, and the feelings she has toward this fruit may change with time.  We often find ourselves in situations where we want something so badly we lose our senses, and don’t consider the consequences– this could well be the case for Lowell’s speaker.
White Currants