The Gospel of John is very different from the other three, and they are similar to each other. Is that a problem?
The gospels of Matthew, Mark, and Luke are similar in many ways. They cover much of the same material, have the same general historical arrangement, and use many of the same words. Bible scholar JJ Griesbach named these gospels “synoptic” because they seem to “see together”. However, there are notable differences between these gospels. The presence of such striking similarities and curious differences causes Christians to ask “how can this be” and “where did these gospels come from”? This is the Synoptic Problem.
There are many possible solutions to the Synoptic Problem. First, it is possible that the Synoptics were all drawn from one source, possibly an original in Hebrew or Aramaic. This is a little hard to believe, though. If one gospel existed already, why write more, changing some of the material in the process? Who wrote it, and what was their relationship to Jesus? Why would such a source not be mentioned anywhere in Early Christian literature?