Jesus tells us - within the context of speaking of His betrayer - how we are to approach prophecy: "Now I tell you before it comes, that WHEN IT DOES COME TO PASS, you may believe that I am He." He repeats this two other times (14:29; 16:4) so that we understand that prophecy has its greatest impact on us after it is fulfilled!
God has drummed this principle since Moses' day. The sign of a true or false prophet is whether or not their predictions happen (Deuteronomy 18:21-22). The prophet Ezekiel vividly illustrates this principle. God made him do many strange things, all of which represented points of prophecies, many of which have yet to be fulfilled. God says of him, "Thus Ezekiel is a sign to you; according to all that he has done you shall do; and WHEN THIS COMES, you shall know that I am the Lord GOD" (Ezekiel 24:24).
Dozens of times in Ezekiel, God uses the phrase, "and they shall know that I am the LORD," or a variant of it. In every instance, it implies the subject understanding this after its fulfillment. For example, notice Ezekiel 22:16, where God speaks to the people of Jerusalem about their sins: "You shall defile yourself in the sight of all the nations; then you shall know that I am the LORD."
Most, if not all, of the prophets had little or no idea how and when God would fulfill their prophecies. Daniel is a classic example. Though angels explained the prophecies to him, he still did not understand.
Although I heard, I did not understand. Then I said, "My lord, what shall be the end of these things?" And he said, "Go your way, Daniel, for the words are closed up and sealed till the time of the end" (Daniel 12:8-9).