Some military training is very strenuous, difficult, seemingly impossible, etc. It is designed that way on purpose; the instructors are looking for quitters, those that can't be trusted to complete a mission. They are trying to weed them out, the quitters, the ones that would rather be doing something else, something less strenuous. That brings to mind the old saying, “when the going gets tough the tough get going”.
I believe God checks us out also. One way He does this is through His word, the Bible. Many people may start to study His word and try to learn His truths, but, only a few actually complete the task without quitting. Bible study is tough, demanding, requires discipline, it is difficult and seemingly impossible at first. As in military training, I believe it to be designed that way on purpose. God is looking for quitters, to weed them out, those that can't be trusted to aid in completing His plan, His mission. He can't use quitters. Those that don't quit, He can and does use in His army. There is a spiritual war happening right now and He needs those that have not quit to do battle (spiritually) with His enemies. He needs His soldiers to help lead others towards Him using His truths to do so. How can one do this if they have never learned the whole truth? It's impossible.
So, what can one do? Don't quit studying His word. Study it completely, cover to cover, book by book, chapter by chapter and verse by verse. Do it at a pace that fits you; you know your appetite for study better than anyone else. If you don't understand what you are reading ask God for the wisdom to understand; see James 1:5. If your reading and comprehension skill level needs improvement, seek help for that particular situation. It is out there. Don't stay where you are now, don't keep quitting every time you run into a little difficulty.
2 Timothy 2:3 Thou therefore endure hardness, as a good soldier of Jesus Christ.
2 Timothy 2:15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
“When the studying gets tough, the tough get studying”.