You say or speak something which may not be connected with the topic.
You cite something from a particular writer or written work as quotation, examples to support the matter of the topic. You can cite a poem written by Wordsworth. You never say or speak a poem. In the above text,
“deep and lasting effect” that Apollo had on “many environmentalists — including me" is an extract from an expertly researched and elegantly written cultural history of the space age titled
"Earthrise".