The value chain is one of those buzz words. It refers to a type of analysis that you can do at your company. If a company makes money then it is adding value to something that customers are willing to pay for. All activities that are involved in adding value are therefore important. All activities that do not add value should be subject to review. The results of such an analysis are often useful since it help managers decide which activities are worth investing in and which activities should be minimized or stopped altogether.
This is common sense, and it is Biblical:
Those who work their land will have abundant food, but those who chase fantasies have no sense. Proverbs 12:11