What is the subject of the first sentence?what does "so that" means? What is the role of two last phrase, could you paraphrase it for me?

Question

Just as painted designs on Greek pots may seem today to be purely decorative, whereas in fact they were carefully and precisely worked out **so that at the time**, their meaning was clear, so it is with Chinese pots.

Answer 1

You ask a question about an extremely complex sentence with several dependent clauses, including nested clauses (one inside another).

The subject of the first sentence: I guess you mean clause.

The first clause is (I will remove some extra words to focus on the structure only):

Just as painted designs seem to be purely decorative (so subj: designs, verb: seem)

now comes a nested adverbial clause beginning with whereas:

they were carefully worked out [contrast of seeming decorative]

and another nested clause beginning with so that (means "in order to"):

their meaning was clear [to state the purpose]

Now comes the second part of the pair...just as (clause) + so (clause) [to show equality]

the new clause is:

it is with Chinese pots (meaning the conditions are the same) (subj:it, verb: is)

This is very difficult to follow I know, because the sentence is built with several clauses.