Why are some words of Jesus in Aramaic transliterated in the Gospels of Mark?

There are a few instances in the Gospels where the words originally spoken by Jesus are transliterated . For instance, we see at Mark 5:41 ;" He took her by the hand and said to her, “Talitha koum!” (which means “Little girl, I say to you, get up!”). We also see at Mark 15:34: " At three o’clock Jesus cried out with a loud voice, “Eloi, Eloi, lema sabachthani?” which means, “My God, my God, why have you forsaken me?” One would be curious to know as to why only a few original words of Jesus in Aramaic are transliterated in the Gospel . Did evangelist Mark intend to give certain emphasis by quoting the original words ? What is the Catholic Church's teaching on this topic ?