A rainbow to a natural man.

A rainbow to a natural man is just a spectrum of light produce by reflection upon tiny water droplet.

Tried as they might a rainbow is just a spectrum of light.

But to a regenerated man, the rainbow is the glory of God.

Both saw the rainbow.

But only one truly see it.

Reference:

Ezekiel 1:28
New Living Translation (NLT)
28 All around him was a glowing halo, like a rainbow shining in the clouds on a rainy day. This is what the glory of the Lord looked like to me. When I saw it, I fell face down on the ground, and I heard someone’s voice speaking to me.

Genesis 9:13
New Living Translation (NLT)
13 I have placed my rainbow in the clouds. It is the sign of my covenant with you and with all the earth.

Daniel 2:22
New Living Translation (NLT)
22 He reveals deep and mysterious things
    and knows what lies hidden in darkness,
    though he is surrounded by light.

1 Corinthians 2:14
English Standard Version (ESV)
14 The natural person does not accept the things of the Spirit of God, for they are (A)folly to him, and (B)he is not able to understand them because they are spiritually discerned.