“And how do we know what the early Christians believed? By knowing how they worshiped. And how do we know how they worshiped? We have records of the Divine Liturgy—lex orandi est lex credendi, a principle that how we pray is what we believe.”
It was just a formalized prayer that really has nothing to do with what persons actually believed.
“1700 years ago”? You have copies that can be dated accurately?
No, actually it's not formalized at all as far as the congregation is concerned. Everything in the litrugy reflects the way the Church believes.
“1700 years ago”? You have copies that can be dated accurately?
You can read more about it here
““1700 years ago”? You have copies that can be dated accurately?”
Yes, nearly so. There are a number of fragments of texts of the Divine Liturgies of both +Basil and +John Chrysostomos from the late 5th / early 6th century. I suspect it is because they were and are so widely used. The older Liturgy of +James was never widespread but the oldest complete copy I think is from the 8th or 9th century.
The DLs of +Basil and John Chrysostomos both are derived from the West Syriac Liturgical tradition which was established at Antioch and thereabouts. The earliest versions of these liturgies extant are also from the 5th century.
It is quite literally true that if an ancestor of mine from, say, the year 500 showed up at my parish church for liturgy next Sunday, he’d know exactly what was going on.