LUKE 4:4
Jesus was led into the wilderness and there He was tempted by the devil. He answered every temptation by saying, "It is written."
The Word of God is the sword of the Spirit, Ephesians 6:17 and it is the only spiritual weapon we have and Jesus showed us how to use it.
Jesus being the Word of God Himself, John 1:1, anything He would have said would have been the Word. He could have said 'scram' and the devil would have had to go. But, instead, He quoted the written Word, the same Word we have to use.
That means that the written Word of God is enough for us also. The Word kept and helped Him to overcome all temptation; He set this example for us to do the same.
No wonder the devil keeps us from studying and knowing what God wants us to know and what we can do or say to defeat him.
God's Word is a mighty weapon. Hell shakes when we speak it in faith. The devil and demons know the power of God's Word, so we need to be convinced of it too!