Inasmuch as many have undertaken to compile a narrative of the things that have been accomplished (peplerophormene) among us . . .
The glory of the gospel is this: the very first verse of Luke's Gospel does not open with a statement of those who have compiled a narrative of the things that have prescribed for us, but accomplished among us. Right from the start, Luke is saying: listen to a report, not rules. News, not advice.
Not: Wonderful! Now we know what we need to do!
But: Wonderful! Now we know what has been done for us.
Only the gospel makes the strange proclamation of what God has done to get to us instead of telling us what we can do to get to God. It has been "accomplished among us."