Sometimes I hear skeptics/non-Christians/atheists poke fun at new Christians for not knowing the Old Testament or completely understanding the New Testament. I think it's fair to say that the insults or questions are getting at this: your belief is on this very minimal god that doesn't lineup with the god explained in the Old Testament or even in all of the New Testament; your belief is a fraud, it is fake, simply not justified. What I want to ask is: does a person have to understand the entire bible before he can justifiably claim to trust in the life, work, death, and resurrection of Jesus Christ?
I don't think a person has to understand the entire bible before she can trust in the gospel. Why? Because the person is responding to the gospel that's why. What is the gospel? The Apostles describe the gospel, as I understand it, as the good news of Jesus Christ. What is the good news of Jesus Christ? One, that people by default are in rebellion against God. Two, that people cannot by themselves be good enough to stand before God in a not-guilty position (or put another way they cannot by themselves not be in rebellion against God). Three, that Jesus Christ paid the debt to God on account of his rebellious people. Fourth, now because of Jesus Christ his people can access God, i.e. worship him in spirit and truth. That is the gospel. Put another way that gospel is that God saves sinners. A person can hear the gospel and justifiably believe it without ever opening a bible. Why? Because that is what is required to be a Christian: hear the gospel, then repent, and then trust in Christ to do what he said he will do. That's it. A person doesn't have to respond to an entire reading of the bible in order to be a Christian. Think about this. The Apostles gave the gospel to people for salvation. That is what their audience had to respond to. The Apostles didn't approach a group of people or even one person, get out their old testament scrolls then start reading word for word the entire old testament then ask their audience (if the audience was still awake or even present) what they thought about that reading. Instead, they delivered the gospel. They didn't even deliver the gospel in the same way every time, e.g. Paul's address in Acts 17 is different from his other gospel messages (in style - the basic theme is the same). Well then, why have a bible? Hey, that's a good question.
Why do we have the bible? The bible is a collection of copied manuscripts from the ancient world. People of that time wanted a written record of the oral tradition. I understand that. Let's write it down to have a copy of this oral religion. I think that is why we have a bible. "Stuff" was going on at that time and it was worthy of being written down. Let's remember: back then, things to write on weren't easy to come by. If it was written down, then it was super important to the person or group of persons who wanted a written copy. The Israelites wanted a written history of their people, their theocratic society, to pass on to their children. Even the prophetic books are historical accounts of what was going on in that time of Israelite history. There are very few, if any, straight-up doctrinal books like in the new testament. This same kind of thinking can carry on into the new testament as well although the genre of written record is different in that the new testament is made up mostly of letters written to churches in doctrinal style. The bible is a copy of what was going on orally at that time and place. The bible is an excellent resource for the new and old Christian alike to learn, read, and hopefully apply the instructions written by the Prophets and Apostles. Do we blindly apply them? Not at all. The Christian is called upon by the Apostles to know why you believe what you believe. So, while the new Christian is justified in his belief in the gospel, he needs to go further. He won't find that the bible and the gospel contradict each other. Will he find some things in the bible that aren't tidy? Sure, for example, what does it mean to "live by the Spirit?" What did Paul mean by that? Obviously there are some different answers to that all through history. It's not tidy. However, just because it's not tidy doesn't mean there isn't stronger evidence for some positions over others. What is tidy is the broad them of Christianity. The essentials are super tidy. The non-essentials aren't and I wouldn't expect them to be tidy because they're non-essentials (like what kind of music do Christians play for worship?).
Wrapping this post up, I want to say that the new Christian is justified in his basic belief in the gospel. The gospel has nothing to do with ancient Israel's form of government. The gospel has nothing to do with ancient Israel's dress code, dietary laws, arranged marriages, polygamy, or other recorded historical acts of an ancient people that wasn't necessarily condoned by God. The gospel is that God saves sinners. If the person who responds positively to the gospel then that person is justified in that belief. It is wise for that person to read about the problems and solutions the new testament has in its collection as well as in the old testament just as it is very important for him to read about the author of the gospel: Jesus Christ. The new Christian should read John's historical account of Jesus Christ to further his knowledge of the Hero described in the entire bible that he heard about in the gospel. The new Christian begins on a road she has never been on before. The road is bumpy, but it has a beautiful destination.
Theism as a properly basic belief - highly recommend
What about the OT? It's unethical
OT laws on relations between adults
Can we trust the bible?