This is why I speak to them in parables: verse 13 is best interpreted as the continuation of Jesus’ response to the question raised by the disciples in verse 10. In verses 11-12 he contrasts those who have understanding with those who do not, and now he focuses upon those who are without understanding. As the quotation from Isaiah indicates (verses 14-15), the people do not understand because they refuse to understand.
In many languages the pronoun This is confusing, since it most naturally refers back to verses 11 and 12. To avoid this, translators can follow Good News Translation, “The reason I use parables in talking to them is…,” or say “Therefore I speak to them in parables, because….”
Again, them refers to “these people” or just “people.”
Speak to them can be “talk to them” or “teach them.”
Because is the same conjunction with which Matthew introduces the words of Jesus in verse 11 (not expressly translated there in Revised Standard Version). This Greek word may either mean because or may be used to introduce a quotation, serving as the equivalent of opening quotation marks. Matthew uses it twice in this passage, but it does not appear at all in the parallels in Mark and Luke. This suggests that Matthew here intends a causative force rather than merely a marker of direct discourse. Two observations strengthen this conclusion: (1) Matthew opens this verse with a formula which specifically indicates cause (This is why), and (2) he alone of the Gospel writers quotes directly Isaiah 6.9-10. The parables thus confirm the people’s refusal to respond to Jesus’ message.
Seeing they do not see: the combination of a finite verb form (see) and a participle of the same (or equivalent) verb stem (seeing) is a way of stating something with great emphasis in the biblical languages. In some languages the meaning of the same verb used twice can best be conveyed by adding some modifier, as in “They can see, but yet they don’t (see)” or “They can see, but they don’t really see.” Some translations such as Good News Translation and Die Bibel im heutigen Deutsch use two different verbs. Die Bibel im heutigen Deutsch says “Because they see, but understand nothing; they hear, but comprehend nothing.” Another example is “They can see, but don’t perceive.”
In some languages people will ask “they don’t see (or, perceive) what?” Possible objects can be “what is there (to see)” or “the truth,” or even “they perceive nothing.”
These same problems arise with hearing … hear. “They can hear, but yet they don’t” or “… but don’t really hear” are possible translations. The text adds nor do they understand, which Good News Translation and New International Version reduce to “or understand.” The problem is that it doesn’t really add meaning to the sense of do not see or do not hear, but translators can make it a separate sentence, “They don’t understand at all (or, anything).”
Quoted with permission from Newman, Barclay M. and Stine, Philip C. A Handbook on the Gospel of Matthew. (UBS Handbook Series). New York: UBS, 1988. For this and other handbooks for translators see here .