“If you believe what you like in the gospels, and reject what you don’t like, it is not the gospel you believe, but yourself.”
Perhaps it is best to start with an explanation of what this means. If you read the gospels (or the Bible as a whole) and take what you like and leave what you don’t like, then you are simply affirming the beliefs you already hold. If you come across some passage that makes you feel guilty about sin, you are free to simply conclude that that part must be uninspired. Say you encounter some truth about God that you prefer not to believe—well, there is no reason to start believing it now. It is much easier to just decide that part of the Bible must be in error. You are the authority. You are the source of moral guidance and truth about God. You affirm only those truths you want to believe.
This is a luxuriously comfortable way to read the Bible and many find it rather satisfying. But it will never change your life. It makes the Bible a broken compass, useless for finding truth. All you will find in a Bible read this way is your own little philosophy—a philosophy too small, too prosaic to make any difference in the world.