Garden of Eden was a setup...

[ChristIsLord]

When the words "<this> is like <that>" show up, Jesus is telling us He's about to drop a parable on the disciples (the believer).
Like when "Galileo dropped the apple"
B-Boys lyric so don't bother correcting me on that....just thought it was funny.

The parallels part you have to study the Bible and read it or certain parts over and over before God reveals the connection. Except for when it's clearly spelled out like the Jonah parallel.

The metaphor thing is a lot more complicated for me and requires study and reference from those Bible scholars that are way smarter and more educated than I am on dissecting the Word,(one end of the spectrum), the other end being simply obvious, like the God is my fortress metaphor. And in some cases I just pray about it and let God show me.

Much like flying in IMC where I can't see squat, but I trust my instruments and and keep going (keep reading the Word and ask God for wisdom) and eventually I arrive at my destination.

How would you justify your opinion on a metaphor vs literalism to someone who holds the opposite view? Say, someone who actually believes there was a guy alive inside a whale for three days?

I don't have all the answers, but Jesus talks about Jonah's 3 days in the belly of the whale and I trust what Jesus is validating by referencing it. about it.