Why and how did the narrator bring Ranga and Ratna together?

The narrator had made up his mind to get Ranga married. He knew Rama Rao’s niece Ratna, who had recently come to the village. She was a pretty girl of eleven. She had come from a big town. She knew to play veena and harmonium. She also had a sweet voice. Her parents had died. So Rama Rao had brought her home. The narrator thought that Ranga was a suitable boy for her. He worked out a clever plan to bring them together. Ratna was quite free with him as he visited Rama Rao’s house frequently. The next morning he went to Rama Rao’s house and told his wife that he would send some buttermilk for her so she should send Ratna to fetch it. When Ratna came, he made her sit in his room and requested her to sing a song. In the meantime he sent for Ranga. When Ranga came to his house, Ratna was singing.