What does the cryptic crossword clue "Moralist turning up in front of train wreck (7)" mean?

The definition is "Moralist". The wordplay uses a reversal. anagram of UP + TRAIN = PURITAN; definition: "Moralist" The answer is PURITAN.

Moralist turning up in front of train wreck (7)

Guardian Cryptic #29412 | 7 Across | 2024-06-18 flower