Our goal is congregations with ever-increasing, corporate activity in worship. One of the oldest tools for enhancing this activity, especially in early Protestant traditions, is the singing of hymns in parts. The problem with this is that congregations don't know how to sing in parts. They don't know how to begin to learn. This goes back to a deeper problem, an attitude that musicianship is a mater of talent, of divine gift, of genetics. It's not. It's a combination of two things - discipline and conditioning.
Claude Goudimel gives you both. Goudimel's approach to part writing is, at best, unusual. But it's a conscious attempt to compel a congregant into becoming a musician. His method is simple - give each person a sense of identity with one of the four voices of a hymn. Your identity as a soprano, alto, tenor, or bass is something that has a tangible application in the sound. Your section has a distinctive way it jumps around or honks a note. The best of it all is that this means you don't have to read music to learn, but learning how to sing naturally ends up teaching you how to read.
It starts with the melody, which is usually pretty catchy. This doesn't really pose a problem. The next part that we naturally want to hear is the bass, since it gives us a sense of the harmony of the piece. Theoretically speaking, if you're a bass, there are three possible notes you can sing with each melody note without creating dissonance, since Goudimel's policy is almost always to have the bass note sing the root position of any given chord. But, of course, nobody really thinks in those terms when they're singing. Simply due to the fact that most other possibilities than the one Goudimel writes are awkward and unsingable, it's intuitive for a bass to sing it the way Goudimel wrote it. From the point of view of someone learning, there's simply a distinctive sound that accompanies his identity as a bass. From the composer's perspective, Goudimel simply never (well, hardly ever) writes an inverted chord.
From hereon out, it's pretty simple. You have a soprano and a bass line in place. The rest essentially fills in the blanks. The alto and tenor parts, which would seem to be more difficult since they're close to each other, again, have that intuitive sense of what not to sing because the other parts are already singing it. To dip again into the theory behind it, at any point, either the alto or the tenor is going to be singing a note that neither the bass nor the soprano are yet singing. For the person who's learning, it sounds funny otherwise. To help distinguish between the two parts, either of the two middle parts at any point is going to be doing something melodic, while the other is honking on one or two notes. Simply by virtue of the fact that there are only two possibilities for each voice at any given time, and neither can do both at once, possibilities are limited and parts become intuitive.
What's important to realize is not how it happens but that it happens. Goudimel is forcing people who aren't comfortable with music to listen to themselves, listen to those around them, distinguish notes from notes in thick textures, and identify themselves with a particular sound. This is, perhaps, why the people who usually end up looking down on Goudimel are those who know the most about music. Not all Goudimel hymns are created equal, and most of them are milk. As long as we keep in mind that the meat is, say, Bach, we're on the right track. But Goudimel is good for where we are now - introducing the idea of sanctifying corporate worship. It's a matter of creating better musicians through a delicate mix of discipline and conditioning.