You have an idea to manufacture and sell widgets. At first, you and your partner, let's call him Woz, make widgets in the garage at your home. Eventually, the demand for your widgets grows and you need more space for widget making machines, raw materials and new employees. You find and rent a small building in a nearby industrial park. The owner of the land collects rent from his productive asset.
Eventually, you need even more space and, after making a cost-benefit analysis, decide that it is more efficient to buy your own land and build your own building. It is a wonderful day when the doors open below the sign, "Patrix Widget Company."
In this way, the land, the building, the machinery, the raw materials, the invested capital and the employees are all part of the process to build and sell widgets. Remove the land and building from the equation and there are no widgets produced. Real estate, in this way, is a productive asset.