What does the 'proper of the Mass' signify?

The correct answer, which indicates that the proper of the Mass changes every day, reflects the nature of the liturgical calendar used in the Christian tradition, particularly in the Catholic Church. The proper of the Mass consists of specific texts and prayers that are assigned according to the feast days, liturgical seasons, and celebrations in the church year. This variability is essential for reflecting the themes and significance of each day's liturgical observance, allowing worshippers to engage with the specific readings and prayers that correspond to the particular day or occasion.

In contrast, the ordinary of the Mass, which includes the texts that do not change, remains the same regardless of the day. The importance of the proper lies in its ability to adapt and respond to the diverse celebrations in the church, whether that be a feast day, solemnity, or a regular Sunday. This dynamic aspect of the proper enhances the worship experience, making it relevant and meaningful according to the Christian calendar.