Some people in this thread have mentioned how doctrine develops. Here is how that process was explained by on of the early Saints, St. Vincent de Lerins:
http://www.newadvent.org/fathers/3506.htm
Therefore, whatever has been sown by the fidelity of the Fathers in this husbandry of God’s Church, the same ought to be cultivated and taken care of by the industry of their children, the same ought to flourish and ripen, the same ought to advance and go forward to perfection. For it is right that those ancient doctrines of heavenly philosophy should, as time goes on, be cared for, smoothed, polished; but not that they should be changed, not that they should be maimed, not that they should be mutilated.
[The Church of Christ] keeps this one object carefully in view,— if there be anything which antiquity has left shapeless and rudimentary, to fashion and polish it, if anything already reduced to shape and developed, to consolidate and strengthen it, if any already ratified and defined, to keep and guard it. Finally, what other object have Councils ever aimed at in their decrees, than to provide that what was before believed in simplicity should in future be believed intelligently, that what was before preached coldly should in future be preached earnestly, that what was before practised negligently should thenceforward be practised with double solicitude? This, I say, is what the Catholic Church, roused by the novelties of heretics, has accomplished by the decrees of her Councils,— this, and nothing else,— she has thenceforward consigned to posterity in writing what she had received from those of olden times only by tradition, comprising a great amount of matter in a few words, and often, for the better understanding, designating an old article of the faith by the characteristic of a new name.
