Let me rephrase my question a bitIt would depend on the context. I would take it to mean "I messed up / I got it wrong / I made a (big) mistake" It could also be taken literally if, for example, someone had spilt something all over the table and made everything on it wet.
Yes, I understand "things" is not understood literally here, as a number of physical things. Let's rephrase it: He made a mess of the situation. In other words, I still don't understand what exactly the "of" means hereUsually, if someone is said to have "made a mess of things", the "things" are likely to be NOT physical things, but things such as arrangements, procedures, etc.
eg John tried to reserve a rental car for when we land in Australia, but he made a mess of things (OR: he messed things up) - he booked it for Austria instead.
If the "mess" is actual physical mess, the speaker will often not actually say "things".
eg The dog knocked the stepladder over and spilt paint all over the bedroom floor. It made a right mess.
In "made a mess of beans," the mess is composed of beans. In "made a dress of silk and lace," the dress is made of silk and lace (and other things too, of course).To me, the 'ofs' in 'a plate of gold and silver' and 'a mess of pottage' are different ofs.
'A mess of pottage' is like "a glass of wine", or "a kilogram of butter".
By "made of" I meant that a mess was made of things (not "consists" or "composed", which means the things still exist in their former form), which means there are no things any more, only "a mess" instead.
If I'm wrong, just show me, please, the definition of "of" in "a mess of things"...