
The top image is the text in the GNT and the bottom is the critical apparatus or app. crit. If you look after the // in the ap. crit., you see the Greek word παλιν followed by the Hebrew letter aleph. That's the symbol for a 4th century manuscript known as the Codex Sinaiticus. I've linked to the Wikipedia article for the codex but it's important for my talk that a digital facsimile of the manuscript is available at http://codexsinaiticus.org/. Go take a look, it's a cool site.
And just by way of introduction, the Codex Sinaiticus is a fourth century manuscript that is one of our earliest complete versions of the New Testament. Much of it is now in the British Museum but came there indirectly from Saint Catharine's monastery on the Sinai Peninsula.
Here's a screen shot of the site's version of John 20:21.

Counting down seven lines from the top of the middle column brings you to the greek "εἶπεν οὖν αὐτοῖς πάλιν" or "He said to them again...". Note that in the GNT version the text is "εἶπεν οὖν αὐτοῖς [ὁ Ἰησοῦς] πάλιν" or "Jesus said to them again..." . The brackets around "ὁ Ἰησοῦς"are an indication of some uncertainty about the reading of the "original" text. The Codex Sinaiticus delivers one component of the material basis of that uncertainty. That's digital materiality.
Here's another CS screenshot:

You can see the extent of correction as a second scribe addressed both basic mistakes and subtle issues of reading in the original product.
We can expand the digital materiality of this text by linking to a gold roundel - "small round disk" - in the collection of the American Numismatic Society:
http://numismatics.org/collection/0000.999.51006 . Here's the screen shot of that page:

To the left of the central Jesus you see Thomas reaching out to touch Jesus' wounds. There's also a slightly irregular transcription of the Greek for Thomas' declaration "My Lord, My God" and of Jesus response to the effect that those who have not required such proof are blessed.
Without going into too much detail, disks of this sort are believed to have been produced in Egypt. This piece doesn't come with a findspot but it is reasonable to invoke it next to the Codex Sinaiticus.
It is another materialization of John 19-29. One that combines text and image. It is a projection into physical space and across time of the message that Christian believers who did not have the opportunity to see Christ can be blessed.
These two objects - the Codex and the ANS disk - show that materiality does not remove the reader or viewer from our understanding of how texts worked. These materializations remind us that texts are physical objects that are responded to by people, and that one response is to change the materiality, as in editing the Codex. Certainly, one response is to debate the meaning of a text. The story of the Doubting Thomas is understood by many modern scholars as a statement against those who denied the humanity of Christ, among whom were the Gnostics, active in
Egypt. The ANS disk is therefore part of an ongoing debate about Christ's nature.
The point of this post is not to go into great depth about what the pairing of these objects tells us about the role of materiality in the Late Roman/Byzantine Egypt. Instead, I want to stress that the opportunity to think about that issue with such relative ease arises from acts of independent self-digitization that exist within wider contexts of topically related efforts also engaging in self-digitization. That leads to an environment in which intellectual risk taking is rewarded.
I don't want the series of inferences above to be pigeon-holed into either saying something about the past or about the present. I think we're at a stage of Digital Humanities where we can recognize that we are doing both. We do not know what questions about the past that modern Digital Materiality will allow us to ask, but I bet we're about to find out.