I think we expect that, if a man is to fulfill a prophecy, then the tasks necessary for the fulfillment of that prophecy are going be the major work of his life. In Conan's universe, it is all in a day's work, almost. In Poul Anderson's Conan The Rebel (New York, 1981), it has been prophesied that a legendary weapon, the Ax of Varanghi, will lie hidden for five hundred years but will then be wielded by a Northerner leading the liberation of the Taian people.
As soon as Conan arrives in Taia, it is revealed in a trance before the altar to a priest of the Taian god, Mitra of the Sun, that Conan is to be the Wielder. Conan himself protests that he has been a rover, barbarian adventurer, thief, bandit and pirate. Here, he refers to his exploits in previous volumes and even to earlier events in the current volume. The priest adds that, if he lives, Conan will also be a king, thus referring to events in later volumes. None of this matters. At this stage only, it is his sacred duty to wield the Ax.
Swearing by his own god, Crom, he accepts, expecting "...a glorious fight..." (p. 149). Next, he must undertake a Quest for the Ax which is guarded by monsters. Needless to say, the Quest is successful.
Some practical considerations are allowed to intervene. The militarily experienced Conan does wonder how mere possession of a single weapon is meant to guarantee victory. Might it not lead instead to overconfidence and defeat? On the other hand, the mere word that the Wielder will lead an army ensures that:
"From end to end of the country, boy, man, hale grandsire, strong maiden took weapons..." (pp. 189-190).
The Ax is so effective that it fills him with confidence. When, on the battlefield, he is incapacitated by magic, there is a danger that his army will bolt but, when his friends have eliminated the threat to Conan himself, there is no stopping them. Immediately after the victory, he surrenders the Ax to the Taian leader and it passes from him forever. As I said, all in a day's work.
At the very end of the novel, Conan tells a friend that everything he did was for Belit, the woman he is with at least in this novel; I do not know about the others. He does not mention Crom, let alone Mitra who had sent the Ax.