Generally, the problem is not that the Bible is all that difficult to understand, rather those who read it fine much of what it says hard to accept, so they interpret it in a manner that is acceptable to them more compatible with their own views.
Why this self-delusion? The problem is twofold.
First, God tells us: My thoughts are not your thoughts, nor are your ways, My ways —as the heavens are higher than the earth, so are My ways higher than yours ways, and My thoughts than thoughts” (Isaiah 55:8-9). Why this ? Because God’s thoughts and ways are based on love–concern for others (matthew 22:36-40).
As humans, we are fundamentally self centered; we first think of ourselves. Our natural tendency is to deceive ourselves so we can serve our 0wn selfish interests. (Jeremiah17:9) points out that our heart, our basic human motivation and reasoning is deceitful above all things, it leads us into self deception.
We need to recognize in ourselves this common characteristic of human nature and be willing to change it so GOD can transform us. We need a new way of thinking, a new heart and mind. Our thinking must be changed by GOD’s Spirit so our interests will be focused outward, enabling us to love others as we love ourselves. Timothy’s loving concern for others, Paul wrote, for i have no one like minded, who will sincerely care for your state. For all seek their own, not the things which are of Christ Jesus” (Philippians 2:20-21).