I am glad that the main things are the plain things in the Bible and they are so simple that a young child can understand them but for some reason many adults reject it.
Nope, you'd be incorrect. Note 1 Corinthians 2:14. Not one person receives these things without God, nor can they know them.
The only mystery to me is in trying to understand why people don’t believe God.
The passage above explains as to why. They can't. No one can come to God, man is incapable of doing so; John 6:36 &c. Note John 6:63 as it gives further insight here.
I prefer to believe what God says in His Word the Bible and not what man thinks or says.
I gave you Scripture, not what man has to say. The above is merely an attempt to sound more spiritual in order to dismiss what was given. That, and you'll use the classic mistake of pitting Scripture against Scripture instead of accepting what Paul said only because it shows your stance to be somewhat incorrect.
There is simplicity in the cross of Christ but there is foolishness in rejecting the only way that we can be saved and that is Jesus Christ and Him crucified for our sins.
Second Corinthians 11:3 “But I am afraid that, as the serpent deceived Eve by his craftiness, your minds will be led astray from the simplicity and purity of devotion to Christ.”
Yes, the simplicity of devotion to Christ, not a crayon-ology Gospel. This the above does not support your theory. Please reread Romans 11:33.
Sometimes we make the gospel so complicated that even adults can’t understand it but it is really so simple that a child can know it. The gospel has been described as so deep that a theologian could drown in it yet shallow enough that a child could wade through it. There is nothing that complicated about the gospel of Jesus Christ. It is not so much a plan of salvation as it is the Man of Salvation.
And for you...
Luke 10:21 King James Version (KJV)
21 In that hour Jesus rejoiced in spirit, and said, I thank thee, O Father, Lord of heaven and earth, that thou hast hid these things from the wise and prudent, and hast revealed them unto babes: even so, Father; for so it seemed good in thy sight.
As I said, the simplicity of the finished work of the cross amazes me.
Mic drop
Rather it is more of a worry that folks truncate the Gospel message as you do, simpleton-ize it, and devalue it, showing a sever lack of respect of and knowledge concerning the Gospel. Let's see, you've brought it down to just make a decision and into heaven one goes, right? Slam, bam, simple! Just decide. Right? What a disgrace that is to the truth.
By the way, what is the Gospel? You keep talking about it.
Funny how Paul talks of its depth and how in this Gospel God's ways are past finding out, but you found a verse or two out of context that doesn't even support anything you've said and pit it against Paul's words. You've not disproven Paul, you're only showing you will absolutely not accept what he is expounding concerning the Gospel of Christ in Romans 11:33.
The above text in Luke actually shows you to be incorrect, that is, if God doesn't reveal these truths, they are not understood by anyone.
Again:
Oh, the depth of the riches and wisdom and knowledge of God! How unsearchable are his judgments and how inscrutable his ways! Romans 11:33 ESV
O the depth of the riches both of the wisdom and knowledge of God! how unsearchable are his judgments, and his ways past finding out! Romans 11:33 KJV
Oh, how great are God's riches and wisdom and knowledge! How impossible it is for us to understand his decisions and his ways! Romans 11:33 NLT