The ideal sound for sacred music during the high renaissance was voices alone.
Introduction to Renaissance Sacred Music:
The Renaissance in literature and the visual arts began in the 1300s and was centered in Italy. The Renaissance in music began around 1450 in what is today northern France, Holland, and Belgium. The style that developed in these countries spread to all parts of Europe.
The composers of this northern style, sometimes referred to as Franco-Flemish, most often wrote music in four voices. For many of their Masses and motets, they continued to use chant melodies as one of the voices, but for the first time they did not keep the chant in the bass. They composed new bass lines and placed the chant in another voice above it. They sometimes even abandoned chant melodies altogether, creating completely new compositions.
Occasionally, Renaissance composers used a secular tune as one of the voices in their religious compositions, something that composers of the medieval period would have thought inappropriate. This music is performed a cappella, or without instrumental accompaniment.
See The Renaissance: The Rebirth of Humanism to learn more about the Renaissance music.
Of interest, find out the 100 most important American musical works of the 20th century, presented by NPR.