The relationship of the OT to the NT is highly disputed, even among evangelical believers.  One approach is to read the OT on its “own terms” and to exclude any meaning that we gain from the NT.  There is much to be said for this approach, because great damage has been done in “finding” things in the OT that were never intended by the original author.  To give one example, did the nails in the tabernacle point to Christ or was their purpose to hold the building together? 

On the other hand, many passages seem to be speaking of the future and we understand what the authors were referring to when we read the New Testament.  For example, in Isaiah 9, the prophet declares that a child will come who will rule with justice forever (Isa 9:6-7).  Critical scholars are now joined by some evangelical scholars in declaring that Isaiah was only speaking of his own day (probably of Hezekiah) and had no intention of predicting a future king.  Later on, Christians “re-read” this passage and saw something “greater” in it that Isaiah never intended.  This is the common way they handle many texts that have traditionally been considered messianic.

Tremper Longman III laments this trend, but I submit that he doesn’t help us out at all.  In a section in his Proverbs commentary (2006), he writes:

I also have considerable doubt that the original authors of OT books had a conscious understanding of the future significance of their words.  Perhaps they had a sense that what they were saying had eschatological implications, but certainly not to the extent that the NT authors took it.  It seems that the appearance of Jesus led to a deeper understanding of the message of the OT.  In the light of Jesus’s death and resurrection, his followers read the OT in a new way (64).

Longman rightly recognizes the significance of Luke 24:21-49.  To refresh your memory, while walking with two unnamed disciples, Jesus said:

Luke 24:25-27 (ESV) “And he said to them, “O foolish ones, and slow of heart to believe all that the prophets have spoken! 26 Was it not necessary that the Christ should suffer these things and enter into his glory?” 27 And beginning with Moses and all the Prophets, he interpreted to them in all the Scriptures the things concerning himself.”

Luke 24:44-46 (ESV) “Then he said to them, “These are my words that I spoke to you while I was still with you, that everything written about me in the Law of Moses and the Prophets and the Psalms must be fulfilled.” 45 Then he opened their minds to understand the Scriptures, 46 and said to them, “Thus it is written, that the Christ should suffer and on the third day rise from the dead,”

Longman, however, says this:

Jesus was angry or at least disappointed that they did not know what to expect.  After all, he taught them during his earthly ministry.

He gave them another lesson, a lesson in hermeneutics, which we are to assume convinced them this time in the light of the resurrection.  From this point on, the disciples could not read the OT except in the light of the resurrected Jesus (65; emphasis mine).

In other words, the meaning of the OT changed upon Jesus’s resurrection.  It meant one thing when the authors wrote it, and it meant something else after Jesus came.  Passages like Isaiah 9 were historical descriptions before Jesus came, but after his ministry, they became prophecies of his life.

But that’s not what Jesus said!  He rebuked the disciples.  He said that they should have understood what was written about him.  It’s not that he provided new meaning, but that they didn’t understand the original meaning.

Maybe I can make my point best by re-writing Longman’s paragraph (his words I reject are crossed out; my new words are in italics).

I also have considerable doubt that the original authors of OT books had a conscious understanding of the future significance of their words every detail about Jesus, especially when he would come (1 Pet 1:11).  Perhaps Clearly they had a sense that what they were saying had eschatological implications, but certainly not to the extent that the NT authors took it.  It seems that the appearance of Jesus led to a deeper correct understanding of the message of the OT by those who were mistaken.  In the light of Jesus’s death and resurrection, his followers read the OT in a new the way the prophets always intended (64).

I understand why secular scholars who deny the possibility of predictive prophecy read the OT the way they do (they have to find a way out!). But it is absolutely stunning to me that some evangelicals follow in their footsteps.  It’s almost as if they ‘ve re-written Jesus’s words:

O foolish ones, and slow of heart to believe all of the new interpretations that I gave you of what the prophets have spoken!