at this comment;

"You really are fit for something better. Come, do change your mind. It is not too late. Go into the law.”

Edmund getting offended at this comment of Mary's would only make him an intolerant fellow, one who got offended because people didn't approve of their choice.

Becoming a clergyman was not a 'calling' for those who wanted to become one. It was a profession chosen because it was suitable. In Edmund's position there was not much choice (army, law, politics (?)), and Mary was naming other possibilities.
Also, there was a place ready for him once he became one.