It's not a mystery, as it
is revealed in God's word.
Scripture tells us the answer, ITL ( Ephesians 1:4-6, Ephesians 2:8-9 )...
Only it seems that you don't believe it.
One thing that I would ask of you, is that you don't fault me for drawing my understanding of His words,
from His words.
To me, it's not a matter of "interpretation", it's only a matter of believing
the very words on the page.
Here, try these:
" He that is of God heareth God’s words: ye therefore hear [them] not, because ye are not of God." ( John 8:47 )
" But ye believe not, because ye are not of my sheep, as I said unto you." ( John 10:26 ).
These tell me why someone does not believe God's words, and why they do not believe on Christ as their Saviour.
I would hope that you both see and understand the significance of these, as well as many others.
At this point, instead of being
selective with what you believe ( at least that is how
I see you treating Scripture ) about the Bible, perhaps you might consider
all of His words as being
equally true ( Matthew 4:4, Luke 4:4 ).
For example,
John 3:16 is just as true as Acts of the Apostles 13:48, as well as 1 Timothy 2:3-4, 2 Peter 3:9 and Romans 9:14-18.
In this case, your # 2 would apply as on the surface, there are seeming contradictions in these passages when compared to each other.
As for your # 5, I would
never accuse you of that.
Understanding God's word is both a matter of study ( 2 Timothy 2:15 ), and a matter of having the Holy Spirit in one's self ( 1 John 2:20-27 ).
It has
never been a matter of not being "intelligent enough" to understand the Bible, for
many intelligent men keep misunderstanding it ( Matthew 11:25 ).
It has always been a matter of God choosing to reveal Himself and His word to someone.
Keep studying, good sir...
He's revealed His Son and your need of a Saviour to you, so trust that He will reveal other things to you as well.
As it stands, He has
many precious truths to share with you.
I wish you well... and may God, in his kindness, give you
many good and lasting gifts.