The similitude concisely compares two concepts, often using something typical from everyday life to something much larger. There is no narrative story. The comparison simply attempts to explain something, often heavenly, by putting it into terms most people can understand. To explain the kingdom of God, the Bible presents a parable in the Gospel of Mark, that the kingdom is like a mustard seed, the smallest of seeds, which can grow into the largest of shrubs.
An extended comparison offers a more detailed version of a similitude, in that it uses comparison in the attempt to teach a moral or spiritual lesson, but still, it has no narrative. The parable of the sower, mentioned in the Gospels of Matthew, Mark, and Luke, compares four groups of people. The first three are unable to successfully sow seeds, because either birds stole them or because they were on rocks or thorns and could not take root. The fourth group planted their seeds on good soil and received an abundance of food. The lesson being that the word must be planted on fertile ears to truly blossom.
The narrative parable tells a short fictitious story, typically of a one-time event. It never indulges in the fantastic, but remains true-to-life. The fictitious story teaches the reader or listener a lesson through comparison. For example, the parable of the two sons in the Gospel of Matthew compares one disobedient son and the other who loves to talk a good game. But when the father asks the two to work in his vineyard, the disobedient son refuses, but eventually feels bad and does his job, while the other lies and never shows up.
The exemplary story tells a fictitious or real tale with an implied moral lesson, but unlike the narrative parable and the similitude, the exemplary story does not present an analogy. The story offers simply an example, one specific case, which illustrates a conduct to be emulated or avoided. The story of the good samaritan in the Gospel of Luke, tells the story of a man robbed and left for dead. Two religious leaders pass by, refusing to help him. But the third man, a despised Samaritan and enemy of the man, helps him. The lesson being to love your neighbor as yourself.