what are the difference between lake and mirror important in this poem?

The mirror essentially becomes the lake. The mirror imagines itself as a lake. A woman looks into it, trying to discern who she really is by gazing at her reflection. Sometimes, the woman prefers to look at herself in candlelight or moonlight, but these are “liars” because they mask her true appearance. Only the mirror (existing here as lake) gives her a faithful representation of herself.