What does "turn" mean in this context?

Question

I understand the quotation from poem "If" by Rudyard Kipling, but I don't understand the meaning of the word "turn" in its context

If you can force your heart and nerve and sinew to serve your turn long after they are gone

Answer 1

Serve one's/its turn is an idiomatic expression that means:

• Be useful or helpful:

  • now that they have served their turn, cut some of them out suppressing his ire would hardly serve his turn at this juncture

(ODO)

• it's a passage about how a person's willpower can win over the weaknesses of the flesh.