22,23 Feb -- Salt with The Last Supper

The readings for Thur 22 & Fri 23 February are -- Gen 11:1-12:20; Ps 5:1-6; Prov 1:15-16; Mt 5:13-32.

Following on from yesterday, here is some more about salt from "A Way Through the Wilderness" by Jamie Buckingham.
"Leonardo da Vinci caught this concept in his painting of the Last Supper. All the men sitting at the table with Jesus were men of loyalty -- all save one. On the table in front of Judas was an upended salt shaker, its contents spilling onto the cloth. It was the perfect symbol of broken Covenant." (Page 83.)
I tried to find a high resolution picture of The Last Supper on-line to verify this. It's very indistinct, but there is something on the table in front of Judas' hand. (Go to www.en.wikipedia.org/wiki/The_Last_Supper_%28Leonardo%29 and look at the section at the bottom headed "External Links". Then click on "The Last Supper - High Resolution Zoomable image", which takes you to the painting at www.elrelojdesol.com/interactive-paintings/the-last-supper.html As an alternative, under "External Links", click on "HIGH RESOLUTION cropping of The Last Supper", which takes you to the picture at www.kaleb222.uw.hu/LASTSUPPER_ENHANCED.jpg )
Judas is in the group of 3 at Jesus' right. He is the only one in the painting with his elbow on the table -- bad form even back then! He has a blue robe and is holding a money bag in his hand. Take a look on the table just in front of that hand.

Here is what Buckingham says as he concludes that chapter.
"Salt is composed of two elements that, if taken separately, are poison: sodium and chlorine. Either will kill instantly. But mixed together, these two elements form an ingredient absolutely essential to life. The wilderness experienced by itself kills. But the wilderness experienced with others brews a recipe of hardy nourishment. Such is the covenant of salt." (Page 84.)

I think he's onto something with all this. But still trying to think it through. The usual interpretation of "You are the salt of the earth" emphasises the Christian's role in the world (preserving, purifying, flavouring etc.) What is said next about being "the light of the world" (especially "let your light shine before men...") reinforces this. The focus is on our witness in and to the world. Yet Buckingham's comments on salt seem to redirect the focus onto the relationship between Christians (and with God)! Before I preach on it I obviously need to get that aspect sorted in my own mind. Any suggestions or comments or insights?