This is the gospel of the Lord:

Romans 10: 9 That if you confess with your mouth, "Jesus is Lord," and
believe in your heart that God raised him from the dead, you will be
saved. 10 For it is with your heart that you believe and are
justified, and it is with your mouth that you confess and are saved.

The Apostle Paul re-iterates again to the Corinthians :

1 Cor 15; 3 For what I received I passed on to you as of first
importance[a]: that Christ died for our sins according to the
Scriptures, 4 that he was buried, that he was raised on the third day
according to the Scriptures,

What Paul, who was given a first hand account, By Jesus, about the
gospel, says of anyone who preaches "anything other." :

Gal 3:  8 But even if we or an angel from heaven should preach a
gospel other than the one we preached to you, let him be eternally
condemned! 9 As we have already said, so now I say again: If anybody
is preaching to you a gospel other than what you accepted, let him be
eternally condemned!

Not really seeing anything about "hidden knowledge" to get into
heaven.  Seems to be out there in the open.

JESUS IS LORD....PERIOD!

Ed C