Bible (The Word)

John 1:1
In the beginning was the Word, and the Word was with God, and the Word was God.
NKJV

John 8:31-32
"If you abide in My word, you are My disciples indeed. 32 And you shall know the truth, and the truth shall make you free."
NKJV

John 14:21
He who has My commandments and keeps them, it is he who loves Me. And he who loves Me will be loved by My Father, and I will love him and manifest Myself to him."
NKJV

Isa 55:11
So shall My word be that goes forth from My mouth; It shall not return to Me void, But it shall accomplish what I please, And it shall prosper in the thing for which I sent it.
NKJV

2 Tim 2:15
Do your best to present yourself to God as one approved, a workman who does not need to be ashamed and who correctly handles the word of truth.
(NIV)

No one could stress enough of how important it is to know the word of God (Old testament and New). The Bible says to be ready in season and out. I cannot tell you how many times I have recognized false teaching from Pastors/Priests because I knew what the Bible taught, and I just have a habit of "testing" the spirit.