1) after adding the carrots to the sauteed onions, ginger and garlic it says to saute for one minute. What does a one minute of sauteing do ?
You often see this in recipes when adding liquid after adding the main is a later step such as with rice pilafs or even some lentil dishes. I guess the idea is that little bit of frying with the aromatics in the hot fat allows their flavours to permeate the carrot better. Would the dish turn out radically different if you didn't saute the carrots? No.
2) the recipe calls for fresh lemon juice but it's only to be added after the soup is cooked and liquidized. What would happen if the lemon juice were added earlier?
Citric juices are often added at the end of cooking for a number of reasons:
a) they are a liquid so they contribute something to the texture of the dish, by adding earlier some of this liquid may evaporate causing the dish not to be as runny (generally fairly negligable though).
b) citric juices are sometimes a volatile flavouring in that their flavour can dissapate if added too early, much like adding a fragile herb too early in the cooking process (such as coriander or fennel fronds).
c) by adding at the end of cooking when the dish is finished it is easier to judge how much juice is actually needed to finish the dish (since citric juices are a fairly potent ingredient) and all the other seasonings are complete.
Hope that helps.