An "instructor" throws knowledge at your wall and what sticks is up to the student. The instructor doesn't necessarily hold the responsiblity for the progress of the student. He does not have a personal vested interest in the individual student. His interest is only in the broad scheme of education. So therefore, he may warn a student who is failing but does not really help or be responsible for the student to succeed. Like in college, it is up to the student to graduate. An instructor is just a provider of knowledge. This is not a true martial art instructor/teacher.
A martial arts teacher, however, is a personal guide for the student. He can show/execute the techniques, one step and a time that he wants you to learn. He seems to have infinite patience. He adjusts his teaching to the individual so that the student progresses. He looks out for the student's well-being and best interests and trains his weaknesses and strengths. He gives help when needed and encourages and maybe praises his strengths or progress. He does not show favoritism or partiality in any way except for health, ie. giving someone easier standards to some and not to others.
A good teacher never stops learning himself. He is constantly upgrading his skills and knowledge. He introduces innovative teaching methods to learn differently. He makes learning the martial art fun. He has a good attitude and may even be entertaining while the rest of us are in pain.
And not least of all, a teacher should be a role model of what he is trying to teach not only physically, but mentally. He should be a person that can be respected and trusted-- a person who has integrity and humility.
I think the last part is the most important part of all. Because without it the "teacher" becomes just an instructor. TW