Which aspect is crucial to understanding medieval church music?

The codification of music by religious authorities during the medieval period is essential for understanding church music because it represents the transition from oral traditions to written forms of musical notation. This shift was important as it allowed for standardized practices in worship, ensuring that specific chants and hymns could be consistently taught and performed across different regions and communities.

As music became more formalized, it was organized into specific categories, such as Gregorian chant, which played a significant role in the liturgical practices of the church. The establishment of these notational systems, along with guidelines on how music was to be performed in worship, shaped the development of church music and its influence on Western music as a whole.

The other options focus on aspects that, while relevant to music history, do not capture the fundamental importance of codification in medieval church music. The use of instruments in worship was limited during this time, and the scoring of operas didn't emerge until later in music history. Additionally, while the development of complex polyphony is significant, it occurred after the initial codification of music, which laid the groundwork for such advancements.