Howdy Robert,
We (born anew believers) become holy, perfect, and justified (just as if we did not sin) when God puts us spiritually in Christ.
Therefore the command "be perfect" is something achievable. Just as "be reconciled" is something achievable. The whole effort to claim God gives us commands that we cannot achieve is bogus, fake theology.
No verse or passage says the gospel is foolishness to all natural men. As I said before "the things of God" refers to spiritual meat in 1 Corinthians 2:14, not spiritual milk. 1 Corinthians 3:1 clearly teaches men of flesh can understand spiritual milk.
All men refers to all humankind.
John 3:3 teaches we must be born anew to enter and therefore see heaven from the inside.. Lots of people reject the gospel, and then some (a few) subsequently repent and fully embrace the gospel.