Don Luis is determined to be a clergyman. It is his earnest desire to answer the call of God and enter into the priesthood. One might think that most people would be happy for the young man, as it's not always the case that someone of his age knows exactly what direction they wish to take in life. But in actual fact, the general attitude of the common folk is one of complete incomprehension.
As Don Luis tells us, there's no one around who can understand what they dismissively describe as his "caprice" of entering the priesthood. With "rustic candor," the common folk tell Don Luis that becoming a priest is a bad idea.
It may be alright for a poor young man, but not for a young man such as himself, whose father is about to marry a rich widow. Don Luis is a young man with prospects, a man who's going places. And so the common folk simply can't understand why he would give up such a charmed life and take Holy Orders.
They believe that instead of entering into the priesthood, Don Luis should find himself a nice young lady, settle down with her, and give his old man half a dozen "handsome and robust" grandchildren.