Prophecy is God’s elucidation, of a small portion of His exhaustive definite foreknowledge, to the human soul.  According to William Burt Pope, this elucidation follows an enigmatic pattern he calls the Law of Reserve:
All prophecy is under the Law of Reserve; a mysterious law which has been appointed in the Divine counsel, and has literally never been changed.  In its absolute supremacy it governs the development of revelation; this being the difference between time and eternity, that in the latter alone will all restriction be done away.  Neither what nor what manner of time has ever been fully made clear until the day has declared it.  It is evident that this might have been otherwise.  The same Spirit Who foreannounced the coming of the Christ could have so described His Person, so unfolded His work, and so defined the period of His advent, as to remove every vestige of uncertainty.  But this was not His will.  He so ordered every prediction, and every cycle of predictions, that, while enough was declared to encourage hope and excite desire, enough was concealed to shut up the heirs of prophecy to faith.  Looking back upon the long series as irradiated by the light of Pentecost we see that every general and every more particular prediction had its determinate reference to the Great Fulfilment; but we can see also that not one of them was clear enough to preclude unbelief in the case of those who were disposed to murmur against Divine Providence.  Every generation could rejoice in the fulfilment of the prophecies that had gone before concerning itself; but as to its own future it was under the sway of an indefinite hope.  There is no exception to this law throughout the economy of prophecy.
In connection with this mysterious law, See Also Section 10.12 of Theology Corner.