Prov 25:2 It is the glory of God to conceal a matter, But the glory of kings is to search out a matter.
Of course, God wants everyone to know who he is and that he loves them but love requires we have an option to love and cannot be forced. If God wanted to make absolutely sure we knew he was there can you imagine his options. One I might think of is that he would write in the sky for everyone to see "tomorrow there will be an earthquake at 9am - God". The next day he might write "Told you so, believe in me or I will send another". Of course, this would not convince everyone, but you get the idea. If God wanted us to know for sure he absolutely existed he could arrange that. What God wants is for us to find out about him, what he has done and is doing for us and the future he has planned for us. God wants us to find him and love him of our own free will. Everything that is needed to do this is in his word but he has not written it such that it would force us to love him. Instead, it is written with the special things hidden for those seeking him.
So although there are amazing mysteries and teachings in the Bible God has written his word in such a way that the reader is not necessarily compelled to believe them. His word designed in some ways not to be understood by those that are not truly seeking to find God in them. Those who meditate on God's word will reap the rewards. Jesus preserves the best teachings for his disciples and then it is his disciple's work to teach others thus making new disciples.
Mrk 4:34 and He did not speak to them without a parable; but He was explaining everything privately to His own disciples.
Jesus always talked in parables to crowds and explained his parables to his disciples. Disciples followed Jesus, sat at his feet to listen, obeyed him and consider Jesus their master. These are the people who learn the mysteries of God.
Luke 10:22 "All things have been handed over to Me by My Father, and no one knows who the Son is except the Father, and who the Father is except the Son, and anyone to whom the Son wills to reveal Him."
So why are so many teachings in the Bible hidden just below the surface of the text? Because that is one of the ways God keeps truths from the insincere and preserves the depths of his word for his followers--his disciples. But the secrets are even further hidden and to be discovered to those who search and investigate God's word. Those who desire to know God. Notice below how God came to Daniel after Daniel sought out God...
Dan 10:12 Then he said to me, "Do not be afraid, Daniel, for from the first day that you set your heart on understanding this and on humbling yourself before your God, your words were heard, and I have come in response to your words.
I explain this to people who sometimes try to understand some of what I present by just taking a quick simple look at the scriptures. I've found that it is usually only after more than an hour of deep study of scriptures that the greatest insights are encountered. Deep understanding of God's word is not only preserved for his disciples but only for the times when his disciples are truly seeking to know him. Dig intently into the study of God's word and prepared to be amazed.