From the beginning of the poem, the persona informs us that she (assuming the persona is a girl) has not eaten fully for quite a while: "all the years". However, now it is time for her to eat - at noon. She takes a rather tentative approach to the table possibly because she is scared that this room that holds the food is too good to be true. Scared that if she might make a sudden move, this room might disappear. Other possibilities to why she's trembling might be the anticipation of actually eating the food or the fact that she's so hungry that she's physically trembling. Either way, she touches the wine glass cautiously, giving me an impression that she hasn't seen wine before: "curious".
In the second stanza, the persona tells us her thoughts on food. She looks through windows at the tables of food whenever she's "turning, hungry, lone". Wealth, in this poem, means two things: one being material wealth such as mansion, furniture, and money. The other is food. Looking through a window from the outside, food to her is "wealth". From this I deduced that the persona is extremely poor to be out on the streets - a homeless person.
The third stanza supports the assumption I made in the previous paragraph "shared in Nature's dining-room". Nature's dining-room is the outside world of the streets, where homeless people eat and sleep. Ample bread is so foreign to her that she is in awe and wonder of how large the bread is. The amount of food she eats is of a crumb, similar to the way birds eat - pecking at crumbs on the ground.
This fourth stanza is where the change occurs. She has fully eaten for the first time and discovers that "the plenty" hurts. This is because she/her body is not accustomed to the amount of food she has eaten and thus, the result of her