Prophets come in two types. There are those who are actually sent on missions, and then there are those who have no particular mission. Their prophecy is given to them as a simple gift from God. The prophet has the advantage in being able to be close to God and to experience Divine ecstasy!
He has no other reason to receive the prophecy other than a reward for his effort in his work in striving to become holier and to cleaving to God. The Ramchal continues to teach us something else about prophecy. While a prophet sent on a mission may well know what he is doing, he may well also not know exactly what he is doing! As a result, he can come to make a mistake or end up considering the prophecy a certain way when in fact it is not that way at all!
Nevertheless, in hindsight, one can see clearly that the prophecy that is given to the prophet can actually go both ways. A prophet’s duty is to ultimately attend to whatever it is that God wants from him. This – if he is being sent on a mission. For the rest of the prophets, they engage in the practice of prophecy to delight in God and to be merit revelations that will assist them in their lives in this world – ultimately to be granted further holiness and a closeness to God.