Paul's whole argument here is that they knew Him but dint believe, dint give Him the glory. But nobody can understand the facts of the gospel see
The natural man recieveth not the things of God indeed he cannot [except you say he can] they are spiritually discerned.
No, Paul's whole argument is that God created us with the ability to know and understand God....it's built into our very being. Men from the very beginning have sought God and believed in Him....from the very beginning. So saying men can't know God or don't ever seek God or can't understand God is wrong. Paul is talking about the deeper wisdom of God not the fact that there is a God or that we are quite able to seek Him.
1 Cor. 2:7
But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory:
We don't need to know all the facts to be saved. That knowledge comes as the Holy Spirit opens the Word to our understanding. What preaching the Gospel does is it lifts up Jesus Christ, like Moses lifted up the serpent in the wilderness. Moses told the people to look upon the serpent and they would live. Those who believed, did. Those who trusted in something else, didn't.
Here's the hook and the dangling worm. The Word itself has POWER when it reaches the ear of man. It calls and draws us to the light.
John 3:16
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
Here's just one example of what the Holy Spirit uses to convict the heart of sin, and a word about how
all men sin and come short. People identify with that, for they know it in their inner most being (conscience). All men have one, and God uses it to convict us of sin.
All men are drawn to the light by the preaching of the Gospel. Those who love darkness turn away, those who have followed their conscience are given more light....which leads to their change of mind (repentance unto salvation.)
Explain how you came to understand the cross? or the virgin birth? or the resurrection? Now I believed these things all my life, I was brought up believing them, it never at any time occured to me that they were not true...but this is not the faith which saves.
Hearing the Word preached or reading the Word brings conviction, and trusting brings the indwelling Spirit. That step of faith is small, but it must be taken. God reaches down to us, but we must reach up to find salvation. We don't need to know everything....we just need to LOOK...to COME, and He does all the rest for we are His workmanship not our own.