Hi Shana,
What a lovely introductory sentence!
Lexically-speaking I’d say both sound natural in that sentence, it just depends largely on what exactly you wish to express.
When I hear ‘Peace and development, ECHOING the themes of the times..’ I understand that it’s an ongoing situation and extends further than the moment we’re speaking of, perhaps continuing into the future.
When I hear ‘Peace and development, REFLECTING the themes of the times’, I understand it to mean that it’s a moment presenting ideas from the past which might not continue into the future.
Personally as a reader, I feel ‘echoing’ sounds better to my ears.
However that’s the beauty of writing, you get poetic licence and get to express your ideas freely regardless of what might be considered more accurate to others.
Happy writing :)