Prior to the Reformation and even in today’s Roman Catholic Church, clergy were/are not allowed to marry. The choice was clear; you could either get married or serve God in the church as a priest. This excluded a number of people with genuine calls of God, yet who did not have the gift of celibacy. It was a requirement the church had put upon candidates for the priesthood that scripture did not. Even before
Luther’s time, there were those who were against this prerequisite.
Those who were already priests, but lacked the gift of celibacy, because they could not marry, often had mistresses and children by them. Though this ran counter to their vows, it was overlooked. With the reforms of the 16th century, one did not have to choose between a spouse and service to God. For many today, it is why they have left the priesthood in the Roman Catholic Church. It is a distinct advantage the Protestants have with this freedom. This is one I am personally grateful for!