Mr. Collin's, who is a cousin to the Bennet's, is a clergyman. At the time of this novel, a man of the clergy would have to earn a "living" from a wealthy family that maintained a local village church. The wealth of the clergyman was dependent on the wealth of the living, i.e., the family. In Mr. Collin's case, he has been "so lucky as to earn the patronage of the honorable Lady Catherine de Bourgh." In other words, he has found himself a profitable living. This is why he is so surprised at Elizabeth's refusal of him. He is adequate or even above her station in life, and therefore should be acceptable (love not being a consideration). This is why Charolette Lucas is so content to take him as her husband. He provides her with a comfortable life:
- "I ask only a comfortable home; and, considering Mr. Collins' character, connections, and situation in life, I am convinced that my chance of happiness with him is as fair as most people can boast on entering the marriage state.” (Chapter 22)
He is a clergyman. Of course, you could say that his "other profession" is trying to get married to a Bennet girl...