The bible says many things which are simple to understand. Often the greatest difficulty understanding the bible is that we wish to fit scripture into our theological system rather than create a theological system around scripture.
The issue which makes theology difficult is that scripture is highly rational and also highly paradoxical. Throughout the bible there is a large amount of rational argumentation appealing to reason. There are also many paradoxes and tensions in scripture.
You see at many times especially in the teaching of Jesus ideas held in tension. There is no contradiction in scripture, but the nature of reality is that many truths are a balance between two extremes which are errors.
We often get scripture wrong because we expend massive effort to simplify it's teaching into a rational system with no tension or paradox. Scripture actually is far easier to understand on its own terms: a system of highly rational belief which also has many tensions and paradoxes within.
It is always the call to wisdom which appears in scripture. You see there is a great nuance to life. You cannot go out and live ethically based on a set of rules without thought and prayer and discernment.
We are often such poor readers of scripture because we come to scripture to learn. We have a certain way we learn. And we fit scripture into our patterns of learning.
Rather we need to first come to scripture to learn how to learn. We must base our efforts to learn around the way in which the bible wishes to instruct us. The bible often does not like easy answers to certain questions, so we must too not like easy answers to questions.
What the bible finds important we must find important. Where the bible offers liberty we must offer liberty. You see the bible is right even when we think it is wrong. We must seek understanding by faith.