The Bible, being a spiritual book, is locked and cannot be unlocked by the human mind - by itself. I Corin. 2:6 - 16. That is until the Holy Spirit gives light, revelation and understanding. The natural man cannot understand that which is spiritual.
God is spirit (John 4), and only the Holy Spirit reveals Him to fallen man. This is why Paul so often spoke of the need for revelation, e.g., Eph. 1:15 - 17, and how he only came to his understanding of thing by revelation.
This is why for the believer who continues to seek the Lord, the Bible never ceases to give new insights (NOT new “truth”) into who God is, who Jesus Christ is, and all that was done on the cross and the depths of His love for us. We will never know God fully, and it will take all eternity for Him to reveal Himself to us. Yes, when we see Him face-to-face, we will know Him in a fuller sense - but still, as He is God, His depths are infinite.
So even we who know the Lord must always, when reading scripture, approach His word humbly, confessing our need for the Holy Spirit to open the “eyes of our understanding”, depending wholly on the Holy Spirit to teach us and let us see what is hidden from the natural eye and the natural mind.
Much trouble has come in Christendom from men approaching and using scripture with their minds apart from the Holy Spirit - with the most common result being division amongst God’s people......”I have the truth......and you don’t......”, or “I see, and you don’t...” being the attitude. Like that of the Jews & Pharisees in John 9:39 - 41.