One is tempted to argue that the whole issue is hopelessly confused and it is best to approach the gospels as they are written and not really worry about the differences. While this is a noble sentiment, it leaves the question of differences unanswered. There are differences that we must account for in some way, either by a dependence theory (2 source, 4 source, etc.) or an independence theory. In his excellent introduction to the Synoptic Problem, Mark Goodacre suggests several reasons students of the Gospels should think through the Synoptic Problem.
Historical and Apologetic Reasons. The order of the writing of the gospels is valuable simply because it is an historical question that is at the very roots of the Christian story. It is sometimes thought that the earliest Gospel is the more “primitive”, before the later theological layers were added. Therefore it we read Mark, or Q, we are reading the earliest strata of Christian thinking. While this has some merit, it is not true that the later gospels are somehow less valuable than the earlier for the sole reason that the demonstrate theological development. It is obviously true that John is more theologically nuanced that Mark, but that does not mean that John is necessarily creating stories and making Jesus say and do things that he did not say or do.
There is an apologetic value to this form of research. It is sometimes objected that the Gospels contradict one another, therefore they are to be entirely doubted. Rather than contradictions, the synoptic variations are to be explained by a literary relationship that can be tracked through the three gospels and in then in to later texts. It is not as though we have to make up crazy explanations for obvious contradictions, the parallels are quite close, just to sort of thing you would expect if there was a literary relationship.
Theological Reasons. It is possible to track the development of thinking about Jesus, who he was and claimed to be over the four gospels. What did Jesus do on the cross? What did he think would happen when he died? What is the importance of the resurrection? This is aided greatly by the synoptic tradition. For example, Mark has the least to say about the resurrection, Matthew and Luke quite a bit more, John clearly the most.
Goodacre uses the Lord’s Supper as an additional example of this theological development. There are four versions of the words spoken by Jesus when he passes the cup, in each of the three synoptic gospels and 1 Corinthians (Mt. 26:27-28, Mk. 14:23-24, Lk. 22:20, 1 Cor 11:25). Historically speaking, Paul is the earliest of the four, only Paul and Luke use the words “new covenant” – a theologically loaded word. Why is that not in Mark or Matthew? Were there multiple versions of the Lord’s Supper liturgy with slight variations? Would a Jewish community be more likely to understand the “new covenant” than a Gentile? Would Mark be likely to not use the phrase if he were writing to Rome? Is there a relationship between Paul and the writer of Luke?
The evangelical scholar must approach these issues with the assumption that if there was dependence on sources, that dependence was under the inspiration of the Holy Spirit. If Matthew used Mark, he did so in a way that was superintended by the Holy Spirit and can in no way be seen as malicious (i.e., Matthew changed the words of Jesus for some theological reason.) There is nothing about the various solutions to the Synoptic problem that is essentially “against” the authority of scripture or the inspiration or inerrancy of the New Testament documents.
By ignoring the problem and pretending that it does not exist does not help evangelicalism in dealing with criticisms of inspiration. We must be able to explain the data in a way that actually enhances the doctrine of inspiration and glorifies God for the rather remarkable collection of documents we have describing the life and ministry of our Lord Jesus Christ.
Bibliography: Mark Goodacre, The Synoptic Problem (Sheffield: Sheffield Press, 2001), 24-32.