First, let us define the term "one-trick pony." It refers to a creature with one, and only one, talent. Superman has multiple powers, from flying to X-ray vision, while The Flash can only run fast. A vegetable steamer can steam various vegetables, while a rice cooker can only cook rice. You get the idea.
In this case, the "pony" in question is a performer. Simon likens a musician to a circus animal, performing the same trick over and over in various cities.
Yet, the focus on this one action has led to a remarkable result. Rather than die of boredom or burn out, the performer has reached a state of divine perfection and grace: "He moves like God's immaculate machine."
The first verse makes this clear. While "he does one trick only," when he does it, "You can feel the heat of his heart" (and let's pause to acknowledge that small marvel of assonance and alliteration). All of his concentration is focused on this one task, and he is truly enjoying the performance of it.
The second verse repeats this idea: "He’s just a one-trick pony, that’s all he is/ But he turns that trick with pride."
One would assume that there are two sides to this hyper-focused perfectionism-- that someone that good at one thing would be bad at everything else. How many concert pianists, for instance, are also famed for their investment portfolios? How many football players are asked for advice on home repair?
And yet that is not the case. Our speaker, the audience of the performance, is amazed that he himself is not as good at navigating the life he has, the life he has had every day to practice and perfect, as this performer is at his art: "He makes me think about/ All of these extra moves I make."
This creature does "one trick" and does it well... and then has all of its other needs attended to, so he doesn't have to be good at anything else! Meanwhile, our speaker needs a whole "bag of tricks" to get through an average day. So the situation is not fair on the other end, either.
This performer has been given the luxury to hone his craft to the point of nearly holy perfection, then being able to "relax in the wings." Meanwhile, those in the audience, who must do everything, don't get to be good at anything. And so they just wander around, "herky-jerky," doing everything partway and calling it good enough.
Additionally, once the trick is perfected, "that's all a pony needs." How many performers never replicate an early hit's success, yet are lionized and made financially comfortable forever after because of it? And yet the average person changes relationships and careers and homes constantly.
There is a mixture of reverence and resentment here. An appreciation for the wonder that is being seen, yet a jealousy at not having been given the time to achieve it oneself.
There is also some recognition that, no matter how long one would have practiced, one lacks the talent to do what one is witnessing. This acceptance is manifested by the religious imagery: "God," "immaculate," "testimony." Watching a God-given talent can be a somewhat religious experience. And there is a realization that there is a reason beyond rehearsals that allows this creature, and not others, to have some time "in the spotlight."
IMPACT: Simon's performance of the song was nominated for a Grammy. The song went to #40 on the US charts. In his biography, Paul Simon: A Life, Marc Eliot confuses this track's chart position with that of Late in the Evening, which did go to #6, not this track. Anyone can make a mistake, but someone should have realized that Late was not mentioned even though it was the standout hit from the soundtrack.
Next Song: How the Heart Approaches What It Yearns