Manufacturing a warehouse of products would only serve only to fill up the warehouse. Hiring a staff to provide services would only waste money if the staff didn't sell the services.
Marketing is the way a company sells products and services.
Marketing is more than advertising in the local paper. Marketing is a concerted effort to sell more. To sell more you must tell customers why they should buy from you. And why they should buy more today and tomorrow and tomorrow. And why they should pay more than they would pay the competition.