David,

You make a good point, and one I am going to remember and use, about Judas leaving and the others assuming he went to purchase something.  This could not have happened on the actual  "High Sabbath" first day of Passover/Unleavened Bread week.

There were a number of days of getting ready for the Passover that included being in Jerusalem early enough to make ready for the feast.

Some say that the meal Yeshua and his students celebrated was the meal in the evening before dark right before the "fast of the firstborn." Some Jews still have firstborn sons fast on the 14th (which was certainly a day of fasting for the passover lambs, as any who have ever butchered know, as well as the Passover Lamb!) but eat well just prior to doing so. This also helps clean out any remaining leaven left in the food dept. :)  like favorite cereals or pasta etc.

We all have so much more to learn.

Shalom,
Betty W.