Student Question -- "Why don't Jews believe in the New Testament?"

This is a huge question that I can only touch upon here. The short answer is that the physical descendants of Abraham (through Isaac) a.k.a. the Jews are not corporately part of the believing community by God's sovereign decree.

ESV Romans 11:17 But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, 18 do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. 19 Then you will say, "Branches were broken off so that I might be grafted in." 20 That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but stand in awe.

Notice how it was an act of God, yet due to their unbelief. It's a theological concept known as compatibilism--click the word for more information.

There is no need to despair because God is drawing his elect (fulfilled Israel) from all nations, including the Jews. We will be covering a lot of this as we progress through the book of Romans.

I've written more on this here: Who is the Israel of God?

Here is a great page full of information about Israel and Judaism.