There's many definitions of marketing?
Wikipedia: Marketing is a widely used term to describe the means of communication between the company and the consumer audience
Entrepreneur.com: Marketing is a form of communication between you and your customers with the goal of selling your product or service to them. Communicating the value of your product or service is a key aspect of marketing.
Me: Driving traffic as many as possible to your Brand.
Is that it? just traffic? yes indeed. from there on there will be Sales converting those traffic, and there after there's Costumer Relationship Management. On why Marketing is important, is that it's a massive way to introduce your product or service so people who are interested will come to you.
In Marketing who finds who first is important, when someone come to you, you will be consider as an expert or consultant, contrary if you come after to someone to offer product/service the person will consider you as nuisance.
They will likely listen to you when you actually making a pitch in a sales process. Marketing is making the sales pitch easier.