Motif and theme go hand-in-hand in folklore studies, but theme has a slightly different connotation than in daily or literary use.

When I teach college-level folklore classes, I’m intent on my students understanding the difference between motif and theme, and how to use the terms properly to analyze folklore texts. The ability to do so demonstrates the key insight that what’s found on the surface of folklore texts is only the tip of the iceberg.
Recall that a motif is “the smallest element in a tale having a power to persist in tradition.” Motifs are almost always explicit at the textual level, that is, they appear word-for-word in the performance or transcription of the folk narrative (though it’s worth noting that we also use these terms in discussing material culture, such as pottery; motifs would include the most prevalent designs such as spirals or depictions of animals).
In contrast, theme is the abstraction of a meaningful idea or message that the listener, viewer, or reader gleans from the folklore text, or which the teller/narrator might intend to convey. In addition to working with a single text, we can assemble a number of texts from a given genre, list their motifs, and then arrive at an understanding of the main themes that genre expresses.
For example, if I were to tell you some dumb blonde jokes, we’d end up with a list of motifs like hair color, mistakes, and stupid incidents/people. But if you look at the aggregate of dumb blonde jokes, as well as the cultural context in which they emerged, it becomes clear that they’re really about gender. Nobody introduces a dumb blonde joke, however, by saying: “Here’s a joke about gender conflict in contemporary American culture…” For the most part, when you’re describing what a folklore text or genre is about, you’re talking theme. And there are some narrators who will introduce story texts that way…but usually inferring the theme(s) of a text means doing a little digging.
One particularly intriguing case study when it comes to themes in folklore genres is personal narrative. Let’s recall that despite their plots that are unique to the teller (being based on the teller’s life experience), personal narratives count as folklore because they become traditional to the teller over time, and thus we can document multiple existence and variation at work (key hallmarks of folklore). The other important factor is that culture shapes what is deemed an acceptable or entertaining narrative, and thus we can document the existence of themes in personal narratives as another way to demonstrate their traditionality.
As personal narrative scholar Sandra Dolby points out, “the use of themes constitutes creative expressions” (24, italics in original). In other words, narrators deliberately inflect their narratives with themes, in order to convey a number of meanings. Further, there are three main kinds of themes that tend to be expressed in personal narratives:
By creating a personal narrative, a storyteller articulates and affirms personal values along three thematic lines: (1) character, (2) behavior, and (3) attitude. The storyteller chooses events that illustrate themes of characterization, didactic themes (behavior), and humorous or ironic themes (attitude). The telling is the choosing of the theme and the creation of the event. (24)
As Dolby asserts, the literary goal of the personal narrative as an art form is to illustrate the teller’s chosen theme, thus demonstrating something significant about the teller’s personal (perhaps moral) character, or about what the teller’s advice and values in a given situation are, or to convey the teller’s attitude about a given topic. Obviously these themes can be interwoven in the same narrative; advice dispensed with a humorous attitude might be an easier pill to swallow than solemnly (to the border of judgey) given advice.
Thus, with a genre like personal narrative that is more on the idiosyncratic and unique end of the traditionality spectrum (unlike narrative genres like folktale and legend, where given plot types persist across centuries and language barriers), we can utilize themes to point out how personal narratives have folkloric qualities. In contemporary America, for example, we can identify the types of themes that many personal narratives display, which Dolby arranges according to her three thematic lines above:
Among those reflecting characterization of the teller are (1) honesty, integrity; (2) cleverness, wit; (3) bravery, heroism, fearlessness; (4) practicality, business acuity; (5) charm, seductiveness; (6) loyalty, patriotism; (7) generosity or affection; and (8) manliness or maturity. Humorous themes are generally classifiable as involving (1) embarrassing situations, (2) ironic situations, or (3) incongruent occurrences. Homilectic themes intended to elucidate moral lessons are reflected in stories based upon (1) terrifying situations, war-time experience; (2) horrifying situations, cruel events; (3) unjust situations; (4) poignant situations; or (5) practical problems in managing one’s affairs. (28)
These personal narrative themes are unique to this cultural context for a number of historical reasons (for example, Dolby was collecting folklore from people who were alive during the Great Depression, so it’s no wonder that practicality and survival skills in the face of oppressively difficult situations would be considered narrative material; similarly, business acuity would be valued in capitalist societies, not necessarily ones with a difference economic system). Thus, an arrangement of personal narrative themes might look different coming from a different region or era.
If you were to collect personal narratives today, I bet that one or more of the themes listed above would emerge once you started to interpret the texts. Other themes not listed here might emerge as well, such as the tension between group identity and individual identity. Yes, we’re in somewhat subjective territory, but stacking up enough texts with enough motifs will lead to some overlapping interpretations over time. Themes always exist in connection to the values of the groups and individuals articulating them. As Dolby writes: “Such themes are the narrative cores that tie the structural subtypes of the personal narrative to real functional concerns in culture and represent as well identifiable traditions useful in folklore classification” (28).
Every folklore genre has persistent themes that crop up and connect that genre back to the needs and concerns of a given folk group. These big-picture ideas, about what humanity is, what love is, what courage is, and so on, are central to artistic expressions, whether folkloric in nature or not. If there’s no theme to dig a little deeper for, it’s probably not going to be interesting enough artistically for people to latch onto it and transmit/engage with it.
References:
Dolby Stahl, Sandra. Literary Folkloristics and the Personal Narrative. Bloomington and Indianapolis: Indiana University Press, 1989.