Complex sentence: Several scholars have argued, on the other hand, for identifying John the Evangelist and/or John the Elder with John Mark; there is, in fact, a great deal of controversy surrounding the various New Testament people named "John".
Split into simpler sentences: Several scholars have argued, on the other hand, for identifying John the Evangelist and/or John the Elder with John Mark. There is, in fact, a great deal of controversy surrounding the various New Testament people named "John".