It is true that the man limited to his passions (more precise meaning of 1 Cor 2:14) cannot understand the Spirit without God calling him; but God does call. What remains is the response of faith, and not all respond.
I am intrigued by this "outward call", and your quote from the Confession does not really elucidate that. What I see looks comical: God calling everyone ("outwardly", you say) but at the same time winks to some "effectually", and those who receive a call but not a wink are somehow called and not called at the same time. In my simple Catholic mind God either call or He doesn't call, -- no mixed signals.
The message is clear. People cannot understand unless God opens up our minds to the scripture. The only way we understand the call of God is by God opening up our minds. Those who do not believe is evidence that God does not open up everyone's mind for no one would choose hell.
To think that we are capable of making an educated decision is nothing more than humanism.