Margaret makes this assertion in Chapter Seven of this novel to Aunt Juley, and shows through the following quote, a remarkable honesty that recognises the power of privilege and wealth to give people like herself and her sister the opportunity, time and luxury to debate and pursue liberal ideas. Note what she says:
You and I and the Wilcoxes stand upon money as upon islands. It is so firm beneath our feet that we forget its very existence. It's only when we see someone near us tottering that we realize all that an independent income means. Last night, when we were talking up here round the fire, I began to think that the very soul of the world is economic, and that the lowest abyss is not the absence of love, but the absence of coin.
What Margaret is saying is that love will only take you so far, as is shown through the character of Leonard Bast and his tragic end. Unfortunately, it is money that ultimately makes the money go round, and, as much as Margaret does not like the fact, she recognises that it is money and her "independent income" that allows her the freedom to be who she wants to be. The opposite is shown in the way that the wealthy and more powerful are able to prey upon the Basts of this world. Remember how it is a throwaway word from Mr. Wilcox that makes Leonard Bast leave his job, which then leaves him without any employment whatsoever.
From what happens in the novel, the reader can safely assume that Margaret's view is shared by Forster, her creator. However, he does not stop hoping that a better, brighter and more equitable future might be created. Note how at the end of the novel Margaret is planning to significantly reduce her wealth. Whilst Forster might ultimately recognise that it is money that makes the world go round, he seems to offer some hope that love, given the right conditions, might be enough to help the great world spin as well.