There are four documents that quote Jesus, all originally written in Greek - the Gospels of Matthew, Mark, Luke and John. First of all they should be understood as having been written anonymously, and that they were only attributed to the persons whose names they now bear later in the second century. In spite of the attribution of two of them to the disciples Matthew and John, New Testament scholars say they could not have been written by eyewitnesses to the events portrayed - I will give some of the reasoning here:
When Matthew, Mark and Luke are laid side by side and read synoptically ('with the same eye') in the Greek language, it is clear that there is a literary dependency among them. Further study shows that Mark was the first to be written, with Matthew and Luke substantially copied from Mark, but with further sayings material attributed to Jesus taken from another source common to both and now known as the hypothetical 'Q' document. Other research has shown that John is loosely based on Luke but with some material taken direct from Mark. So Matthew and John were not written by eyewitnesses, and it is universally agreed that Mark and Luke were not either, although usually for different reasons. This means that we are unlikely ever to know just what Jesus really said.
When trying to understand quotes from Jesus, it should therefore be understood that none of the gospels is likely to contain verbatim quotes. We do not even know where the 'Q' material came from, but John Dominic Crossan, author of The Birth of Christianity: Discovering What Happened in the Years Immediately After the Execution of Jesus, sees an even earlier Common Sayings Tradition, from which 'Q' and the Gospel of Thomas drew, and which may have been a source of some material in Mark.
Differences between Greek and Hebrew must be taken into account, particularly when English can not properly represent the original Greek. One example is in the different Greek words for love, particularly agape (sacred, or unconditional love) and philia (brotherly love). When the early Greek-speaking Christians read John chapter 21, they would have understood it quite differently to the usual understanding in non-Greek languages (including Hebrew and Aramaic, but also Latin and English). In this chapter, on the Sea of Galilee, the risen Jesus questioned Peter three times, just as Peter had previously denied Jesus three times. Jesus addressed him each time theatrically as "Simon, son of Jonah", not as Peter, the name Jesus had given him.
The first time, Jesus asked , "Do you love (agape) me more than these [the other disciples]?" Peter answered that he loves him, but only using the Greek word for friendly or brotherly love (philia). In exasperation, Jesus said, "Feed my sheep." With the meanings of sacred and brotherly love lost in the English translations, this last statement is usually interpreted as a sign of approval, quite the opposite of the original meaning.
Jesus again asked Peter, "Do you love me?" Again, sacred love (agape), but this time did not ask whether Peter loved Jesus more than the others. And again, Peter replied with the Greek word for brotherly love (philia). Jesus again replied, "Feed my sheep."
In the third questioning, Jesus asked only whether Peter had brotherly love for him (philia). He accepted that this was the most that Peter would give. For the third time, Jesus said, "Feed my sheep."
A reader of the original Greek gospel would have realised that Jesus was frustrated at Peter's inability to say he love him unconditionally, and recognised "feed my sheep" as an indication of his exasperation. For us, the nuances of unconditional love are lost, and the same passage is more usually read as a command, thrice repeated, for Peter to "feed my sheep" - "minister to the Christians" - but this is not what was written.
