A scholar is someone who knows things with an awareness of the knowledge of others. This is why the scholar’s work involves so much reading and writing. In order to know what others know we must have access to that knowledge and writing is the most efficient way of communicating what you know to people who are knowledgeable about the subject. In their writing, scholars tell other scholars what they think and why they think so.
Scholarly writing, we might say, is the art of writing down what you know for the purpose of discussing it with other knowledgeable people. It opens our thinking to criticism from our peers. Scholars are people whose beliefs are constantly exposed to criticism from people who are qualified to identify their errors. That’s the reason we think of them as “knowledgeable”. Their beliefs can stand, and have stood, critical scrutiny by others.