The Israelites were a literate race from their beginning. The Pentateuch has many references to reading and writing. All Israelites were commanded to write the commandments on their hand, as frontlets between their eyes, gates doorposts. (Deut. 6:8-9) There are many references to reading in the Gospels. Jesus only had a carpenter's education but He read in the synogogues as did all the men. He wrote on the ground at the accusation of the woman caught in adultery.
In order to memorize a story or even a statement, it must first be written down. No one can memorize a dialogue with just one hearing of it and without being commanded to do so. Once you can read and write there is no point in memorizing except to allow for circumstances where you do not have access to the written record.
Humanly speaking it is impossible to have an oral record of historical dialogue, for no one understands the importance of an event until well afterwards and then it is too late to remember dialogue accurately. That is why historical records do not record dialogue except the Bible and that because it is divinely inspired.
The Gospels indicate that they were committed virtually immediately to paper Are the words ...let him
that reads understand,
(Mk. 13:14) the words of Jesus or Matthew and Mark, added as an explantion later.
In saying this it implies a mystery, something that may not be easily understood. Now Jesus knows the mystery but
does Matthew or Mark? If Matthew knew the mystery so also would have all the disciples because Jesus did not
explain it further and so we would presume that it was common knowledge to all those of that day but not
necessarily to those of a later time in which case Matthew and Mark saw the necessity of adding these words,
which would be their's and not Jesus.
However if Matthew and Mark knew the mystery, as an apostle they would be bound to tell the mystery, because being presumably, common knowledge to them, yet understanding that it may not be to later generations, they would have the desire to inform them as to what it would be and so they would not add these words but rather give words of explanation as in the case of the interpretation of Jesus words, given as an aside in Mark 5:41.
But assuming they were the words of Jesus because for some reason he did not want the matter of the mystery
to be common knowledge, that is, known to the non elect, makes sense. For just as when Jesus spoke in parables,
he said that he did so, so that the non elect would not understand. Now if the non elect were not to understand
in this instance also, and they don't, who then is able to make such a decision, that they should not be informed
Jesus or Matthew and Mark? Plainly only Jesus could have determined, if these words, ...let him that reads
understand,
be included and also that the invitation of the understanding of the mystery was given not
only to readers but the apostles present as well.
Bear in mind that Luke, the most educated, did not include them. Did he understand the mystery? Would he not be the first to understand? Would he not be the first to realise that later readers would not understand? Would he have seen it as of less importance that the people be warned that they should understand this mystery? We must conclude that Jesus is the one saying these words and that in effect that the next person to know of these words would know of them by reading them. Hence Matthew and Mark must have been written virtually immedately after Christ's death.
(Matt 24:15 & Mk. 13:14) otan de (Matt 24:15) oun (Matt 24:15 & Mk. 13:14) idhte to bdelugma thV (Matt 24:15) to rhqen dia danihl (Mk. 13:14) to rhqen upo danihl (Matt 24:15 & Mk. 13:14) tou profhtou estoV (Matt 24:15) en topw agiw (Mk. 13:14) opou ou dei (Matt 24:15 & Mk. 13:14) o anaginwskwn noeitw (Lk. 21:20) otan de idhte kukloumenhn upo stratopedwnthn ierousalhm tote gnwte oti hggiken h erhmwsiV authV (Matt 24:16, Mk. 13:14 & Lk. 21:21) tote oi en th ioudaia feugetwsan
The words ...let him that reads understand,
(Mk. 13:14)
are the words of Jesus. Jesus spoke these words, the Holy Spirit brought them to remembrance to Matthew
and Mark but not Luke. Matthew and Mark did not insert them on their own initiative.
If it were possible that the sayings of Jesus were committed to memory, because say, Jesus repeated them so many times that they stuck in the mind, there are many other sayings by other minor characters that are still integral with the story yet would never had been committed to memory. The proposition that there first existed an oral record from which later books were written is simply stupidity or an outright lie.
NOTE: It is one thing to commit to memory Scripture for edification but a totally different thing to commit to memory for the sake of record. While there have been cases in history where people have committed to memory large documents such as the Gospels it must be born in mind that these were committed to memory from written documents. Where there is only oral communication it is almost impossible to imagine that extensive histories including dialogue could ever be committed to memory with any degree of accuracy.
In order to have even a slight chance of doing so you would need outstanding teachers and genius students and every time the record was passed down you would need the same. Generally when oral histories are part of a culture they have the status of myth. The Gospels do not have this status.