I always tell people who ask me why I read the Bible everyday that the Bible is to our spirit what food is for our physical bodies. Without reading the Bible you are starving your spirit and eventually it will lead to death of your spirit. You can't be a 'Christian' and know nothing of the Bible, in the same way you couldn't be a Personal Trainer and know nothing about working out and nutrition. It probably wouldn't be long before you got fired from your personal training job and lost all your clients due to incompetency, so why would we want to do the same thing with the most important job we have here on earth- being an example of Christ.
The Word is God and if we aren't in it then how do we know Him? It certainly won't be from sitting in church one day out of a week, maybe two. Sitting in your garage won't make you a car and sitting in church doesn't make you a Christian. That's why there are hypocrites in church that turn people away from God. It's our job not to be one of them!
Well, there's also another very important aspect to why you should do everything in your power to know your Bible front to back. It's simple- we can be deceived by others. Just think about the amount of trust you are putting into someone else's hands to teach you the Word of God if you don't know it yourself. It's real easy for someone to gather up some Bible verses and put them together, make it sound good, and teach you something that is NOT what God is saying at all. The Bible tells us to test all things to see if they are from God. But how can we do that if we don't have a complete understanding to begin with. It's like trying to put a 1000 piece puzzle together without the picture of what it looks like and then on top of that, somehow pieces from a different puzzle got added in the mix. Now your trying to put a 1000 piece puzzle together with no picture of what it looks like and the pieces (information) you have isn't right. Yeah, that should be fun and turn out great, right?
I know so many people who have been deceived by others, by churches, by 'religion/denominations', and by well-meaning people even, so don't be one of them. Make every effort to get to know God and get a real relationship with Him by reading your Bible everyday and know it cover to cover. There's an abundance of liars and hypocrites in this world that will be glad to tell you their version of who God is and what the Bible says, and sometimes those can come in the form of innocent well meaning people.
1 John 4:1 "Beloved, do not believe every spirit, but test the spirits, whether they are of God; because many false prophets have gone out into the world." NKJV