What does the cryptic crossword clue "Looking to the left, further thought surely vital (9)" mean?

The wordplay uses a reversal. PS (reversal="a further thought") + RIGHTLY (synonym="surely") = SPRIGHTLY The answer is SPRIGHTLY.

Looking to the left, further thought surely vital (9)

Guardian Cryptic #29426 | 10 Across | 2024-07-04 flower