"... Spock says that the probe signifies aliens of great intelligence that somehow, are unaware of the signal's destructive nature and that he thinks it illogical that the probe's intention is hostile. When McCoy asks if this is the probe's way of saying hello to the people of the Earth, Spock points out that only Human arrogance assumes the message must be meant for them..."

"...In the Bounty's lab, Spock discovers that it is in fact a whale song, specifically that of the humpback whale. McCoy at first wonders who would send a probe across the galaxy to speak to whales, but Kirk and Spock recognize that whales were on Earth ten million years before Humans. Humpback whales, Spock points out, have been extinct since the 21st century, and so it is possible an alien intelligence sent the probe to establish why they lost contact..."

What I immediately jump to when reading these stories. The movie rates as one of my favorite Star Trek movies because of all the "colorful metaphors"