You cannot be a believer in Christ Jesus unless the word of God is the standard of truth in your life. If there is any wavering about this in your mind, then you have given the enemy a huge advantage to snuff out your spiritual life. The word of God is the actual sustenance our spirits need in order to grow and mature in the faith (Hebrews 5:12).
Many professing Christians are actually not believers at all. Rather, they are beleavers. I call them beleavers because they 'be leaving' the Lord at the drop of a hat. They have not committed to give their life to Jesus. They are not willing to stand with Him against that which is evil. They use Jesus like window dressing to pretty up the outward appearance of their lives, but leave the doctrine of Christ and deny Him at the slightest sign of pressure or conflict.
beleave: to cause or allow to remain behind, to leave something behind; to abandonA lot of time is wasted talking to and trying to reason with beleavers. They spend most of their time disputing the word of God and explaining why it does not mean what it says...and then they'll get mad at you when you point them to the Scriptures.
"They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate." Titus 1:16