Kessler's most striking example was of Jewish commentators comparing Isaac carrying his wood to "a man who carries his own cross". The background is that the traditional Christian reading of the Isaac story is in the context of the Crucifixion. There are various elements that reflect the Passion story, including of course the key thematic element of a father sacrificing his son. There are also important differences, the fact that in Christian tradition Isaac is seen as a child, whereas Jesus is an adult who is fully aware and acquiescent to the sacrifice. Isaac is saved at the last minute; Jesus' sacrifice actually goes the whole way.
Obviously Jewish commentators would generally reject any connection between the (potential) sacrifice of Isaac and the NT story. However, Kessler thinks that some of the midrash is directly countering Christian views of the story, ie the Jewish tradition is aware of the Christian reading, rather than just ignoring it. So where Christians say that Isaac's carrying the wood for his own sacrifice is like Jesus carrying the cross for his, this midrash makes the point that Jesus is not the only person who was crucified.
Both Jews and Christians comment on Abraham's authority to make the sacrifice, and how that plays into their understanding of priesthood. Fascinatingly, both quote the same verse from Psalms: 110 v4 (
The Eternal has sworn it, and will not repent: you are a priest for ever, in the order of Malchi-Tzedek). The Christian writers1 use this verse to show that the priesthood has passed from the Temple priests to the Church (because Abraham took over the priestly role from the pagan priest Melchitzedek), the Jews use the same verse to show that the priesthood remains with the priests (because the Psalm says you are a priest forever). Since both that verse from Psalms and its connection with the Genesis story are pretty obscure, it seems reasonable to assume that the reason the Jewish commentators quoted it was because they were directly refuting the Christian interpretation.
Another connection revolves around the legal technical term συνηγυρία [sinegoria], which is apparently a Greek word meaning defence lawyer.
In the Jewish tradition, Isaac is generally held to be a young man rather than a child, so there is emphasis that he too, and not just Abraham, was willing to be sacrificed. Could this be a direct, if subtle, counter to the Christian view that Jesus was the only person in history who went so willingly to be sacrificed?
Then you get into the really weird bit, which is the Jewish resurrection stories around Isaac. The pshat says that Isaac was never killed, but there's a very persistent and very odd Jewish tradition that says he was in fact sacrificed and then brought back to life. There are lot of references not just to the binding of Isaac, but to the blood of Isaac, or the ashes of Isaac. And Isaac is traditionally associated with the blessing which names God as the one
who gives life to the deadin the Amidah, the main prayer in Jewish liturgy. There is one midrash, (IIRC this is the Pirke d'Rav Eliezer from the 8th century), which goes even further, saying in so many words that Isaac's soul fled from his body at the moment of sacrifice, and when the angel called out to Abraham, he called Isaac's soul back to his body. This is said to be how we know that the dead will be resurrected.
Quite a lot of discussion about how you can draw conclusions from a largely oral tradition and one which was subject to a lot of censorship. The Jewish tradition never directly and explicitly quotes Christian writings, which means that apparent similarities could just be a coincidence, or maybe drawing on a common but unrecorded earlier tradition. Or maybe all the traffic was one way, the Christians were quoting (post-Biblical) Jewish sources but not vice versa. This seems intuitively unlikely to me (I mean, one-way intellectual influences require a highly artificial situation. And why on earth would the Jews have come up with the idea of carrying the wood being like carrying a cross?!), but it can't be formally ruled out on the basis of the very skimpy evidence.
And then of course the consequences for modern Jewish–Christian relations. Kessler pointed out that the Jewish context of the NT is now accepted by most Christian scholars, leading to an effort on the part of Christians to understand Judaism. But what about the other way round? If his examples are to be interpreted in the way he's suggesting, Christian thought was an important influence on Judaism throughout the main period of rabbinic Judaism (first century through eighth century). Should Jewish scholars therefore be paying more attention to Christianity? And what is a good way to engage with Christian influences without letting go of our own, uniquely Jewish, understanding of Torah (and also without imposing our own framework unfairly on Christian thought, as Christianity historically tended to do with Jewish scriptures)?
1] See pw201's comment which expands the New Testament context for this connection.