...is it's had the same structure since the dawn of Christianity.
The basic structure of the Mass is the Liturgy of the Word where we hear the Scriptures proclaimed and the Liturgy of the
Eucharist where we break bread and share communion. The exact details
of how this is done have been refined over the centuries (Vatican II
changed a few things, for example) but the two-part liturgy has been
around since ancient Israelite times.
We see Christ affirming
it on the road to Emmaus (Lk 24:13-35) where he interprets the
Scriptures for two disciples and then breaks bread with them. Right
after Pentecost the apostles devoted themselves to studying the
scriptures and to breaking the bread (Acts 2:42).
bare-bones descriptions to be sure by by the middle of the second
century Christians were worshiping in a way that would've made any
modern Catholic feel right at home. Below is a link to St. Justin's
First Apology. Chapters 65-67 are a great read; see how many elements
from what he describes remain in today's Mass.
That the Mass
has remained structurally the same since the very beginning of
Christianity is yet another reason Catholics are content leaving it