It would be correct both with and without the "a." Having the "a" there just makes it sound a little more poetic.

There's quite a simple answer to this (and it's nothing to do with poetry!). Look at the grammar of what comes next : "a peace and cooperation that prioritizes human beings and upholds the universal values of humanity" is one long noun phrase, including a restrictive relative clause. Anything defined by a restrictive relative clause is specific. So, this is not 'peace and cooperation' in abstract terms: it's a (particular kind of) peace and cooperation that does a particular thing. I hope that makes sense.