Donald Guthrie wrote what is perhaps the most complete and comprehensive introduction to the New Testament. He offers a wealth of information, particularly concerning the Gospels, and apart from treating each individual gospel, writes nearly 100 pages on the Synoptic situation which is commonly called a "problem", which it is not.

I would not suggest buying the book new, at almost $30, when you can get it for just a few dollars at either of the sellers below. I got mine from Abebooks for $3 after shipping.

New Testament Introduction - Amazon
New Testament Introduction - Abebooks

Have you ever wondered why there are 3 Gospel accounts that seemingly say the same thing in many places? If they are saying the same thing, then why are there 3 of them? Why did there need to be 3 of them?  Matthew, Mark, and Luke are commonly called the Synoptic Gospels. There is no doubt that these 3 books are talking about the same person (Jesus), and generally telling the same story. But if they are the same, then do we really need all three of them? Of course! But why?

Then there is the issue of how they were written. Did the Holy Spirit speak to all 3 writers at different times in an isolated way? Or was one of the accounts used by the other two to compose theirs, all the while being led by the Holy Spirit? Luke 1:1-4 seems to tell us this. Which of the 3 was written first then? Mark or Matthew, because it couldn't have been Luke? If it was Mark first, then did Matthew use Mark as a basis to write his account?

You may think these are silly and overly critical questions of little or no importance, but I assure you that they are not. The way you view these issues will impact the way in which you view and understand the gospel accounts, either for the better or worse. These are age old questions, and ones that really do merit our study more than you may think.

If you have ever wondered why Matthew said it this way and Mark or Luke that way, among many other questions, then I encourage you to dive in to the study of these 3 Gospel accounts.

There has been a lot written on the topic already. May I suggest these resources as a good starting place:

Rethinking the Synoptic Problem - Dave Black
Jesus and the Gospels - Craig Blomberg
The Synoptic Problem - Dan Wallace (pdf)
Matthean Priority - Gary Derickson (pdf)
Interpreting the Synoptic Gospels - Scot McKnight