So why do I use the Pāli Canon almost exclusively when trying to understand Buddhism? For many of the same reasons that others do, as it turns out. It is the earliest record we have of the Buddha's discourses in writing and staggeringly comprehensive. Judging by the length of the canonical texts as a whole (which far outstrips even the longest canon of the texts of the Bible), the Buddha would have had to have lived for quite a long time and done quite a lot of public speaking in order for the Buddha and his disciples to produce that many discourses.
It's important to note that the relative age of a text is no guarantee of perfect fidelity to a speaker's message. I have no illusions about that. I do, however, have a sense that the more removed a text is from the speaker (whether by culture, language, or time) the more likely it is to be even less faithful to the speaker's message. And in fairness, the Pāli Canon wasn't recorded until several hundred years after the Buddha's passing on, which is pretty far removed compared to the Gospels of Christianity that were written decades after Jesus' death.
We might reasonably suspect that the Pāli Canon could well be less faithful to the Buddha's teachings than the canonical Gospels are to Christ's teachings, but I tend to give the Pāli Canon the benefit of the doubt since it's the best textual evidence I have. I also tend to give it the benefit of the doubt because it is remarkably coherent both in style and substance. The kinds of repetition recurring across many discourses, both of phrases and themes, suggests that the content of the message is coming from a single speaker or perhaps a group of people very much trying to remain faithful to the words of a single author.
Many people might find it unbelievable that the oral tradition preserved by monks could ever remain faithful to the Buddha's teachings over the course of 400+ years, but there's actually good scientific evidence that human beings are quite capable of preserving accurate information by oral tradition for many thousands of years and then communicating it effectively in a new language. Which is good for assessments of the authenticity of the Pāli Canon, because it's not exactly written in a language that's widely used by native speakers today.
So what language is it written in, and why is that important? I'll cite the translator of the anthology of the canon I've been using for my studies of it in order to explain.
"...the Pāli Canon has special importance for us, and that is so for at least three reasons.
First, it is a complete collection all belonging to a single school. Even though we can detect clear signs of historical development between different portions of the canon, this alignment with a single school gives the texts a certain degree of uniformity. Among the texts stemming from the same period, we can even speak of a homogeneity of contents, a single flavor underlying the manifold expressions of the doctrine. This homogeneity is most evident in the four Nikāyas and the older parts of the fifth Nikāya and gives us reason to believe that with these texts--allowing for the qualifications expressed above, that they have counterparts in other Buddhist schools--we have reached the most ancient stratum of Buddhist literature discoverable.
Second, the entire collection has been preserved in a Middle Indo-Aryan language, one closely related to the language (or, more likely, the various regional dialects) that the Buddha himself spoke. We call this language Pāli, but the name for the language actually arose through a misunderstanding. The word pāli properly means 'text,' that is, the canonical text as distinct from the commentaries. The commentators refer to the language in which the texts are preserved as pālibhāsā, 'the language of the texts'. At some point, the term was misunderstood to mean 'the Pāli language,' and once the misconception arose, it took root and has been with us ever since. Scholars regard this language as a hybrid showing features of several Prakrit dialects used around the 3rd century B.C.E., subjected to a partial process of Sanskritization. While the language is not identical with any the Buddha himself would have spoken, it belongs to the same broad linguistic family as those he might have used and originates from the same conceptual matrix. This language thus reflects the thought-world that the Buddha inherited from the wider Indian culture into which he was born, so that its words capture the subtle nuances of that thought-world without the intrusion of alien influences inevitable in even the best and most scrupulous translations. This contrasts with Chinese, Tibetan, or English translations of the texts, which reverberate with the connotations of the words chosen from the target languages."
The point that it's useful to have religious teachings in a language that would share the same conceptual matrix is one I've made myself in discussions about what language is best for studying other religious texts. It's certainly true, in my experience, that a shared conceptual matrix makes a big difference in the ease of understanding a teaching in a particular language.
It is much more difficult, for example, for me to understand anything in Japanese than it is for me to understand most things in Spanish or French. I actually have more education in Japanese than in French, but the extent of the shared conceptual ground that lies between French and English is much greater than the shared conceptual ground between Japanese and English.
But language is not the only concern, or even my primary concern. I strive to understand religions much more deeply than I can by force of linguistics, which brings me back to citing the translator.
"The third reason the Pāli Canon has special importance is that this collection is authoritative for a contemporary Buddhist school. Unlike the textual collections of the extinct schools of Early Buddhism, which are purely of academic interest, this collection still brims with life. It inspires the faith of millions of Buddhists from the villages and monasteries of Sri Lanka, Myanmar, and Southeast Asia to the cities and meditation centers of Europe and the Americas. It shapes their understanding, guides them in the face of difficult ethical choices, informs their meditative practices, and offers them the keys to liberating insight."
This is an important point for me, because I am striving to understand Buddhism not just as a set of propositions to be systematized and understood, but also as a living religious tradition in which many of my fellow human beings participate. With any religion, it's important to gain a visceral understanding of it and be connected to it as it is actually experienced and practiced by those who are members of that tradition.
I even go so far as to seek out a translator who is also deeply committed to the practice of the religion I study. While this does mean that the translator will have biases in favor of the religion and maybe a specific school within it, the translator's bias as a practitioner is part of the lived experience of the religion which I am seeking to understand. My advice to any seeker after the truth is to start with the textual evidence, but certainly not to stop with the textual evidence.
Those who only seek to understand the words being used in a religion's texts will never understand the religion; they will only understand the words, and the words are just one important part of a whole with many important parts.
CC BY-SA 2.5, https://commons.wikimedia.org/w/index.php?curid=190448
Note: For those who are interested, you can find more information about the anthology I'm using on my Sources page.