I think that one does not have to go far in assessing the statement with the likes of Regan and Goneril. Both of them had set their sights on "the old man's" kingdom for some time. Their flattery, as alluded to in the subtext of the question, is designed to develop a veneer to showcase their "love" for their father. In this light, they perceive "love" and the words associated with it as a means to an end. Both of them understand that this is the way to accomplish their end goal. When Lear speaks to Cordelia about "nothing will come of nothing," it is significant to the older sisters because they fully understand two realizations. The first is that their plan is working and has to continue. The second is that Cordelia can now be seen as expendable as her designs have come of "nothing" in comparison to the older sisters. In the largest of senses, the threat and the entire scene creates a very intense picture of what love is defined as and what it means. Lear associates love with words that flatter and believes that the ornate decoration that might befit a man of his title represents "love," something that Regan and Goneril manipulate to their advantage. At the same time, we see that the love which speaks of "nothing" is actually the most pure and true form of love, and within this, there is a significant threat that Lear issues to Cordelia as a response, but also a threat is present to the older sisters. Regan and Goneril have to work quickly to dispense of Cordelia lest the father realize that the one who spoke of "nothing" actually possessed more than those who professed to speak of "something." When the idea of "nothing will come of nothing" emerges, it is quite telling as "nothing" comes out of Regan and Goneril's affections and the only "something" to emerge is from the one who initially spoke of "nothing."