There are some things that we can expect from the devil. The Bible tells us that we struggle not against flesh and blood, but against demonic forces. Ephesians 6:12, "For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places."
What are some of the things we struggle with?
The first thing is deception. To deceive somebody means to make another person believe a lie or something that is not true. When the enemy sends deception your way, it is an attempt to deceive you into believing something that is not true, so you will fall into error. Strongholds are built through deception. A stronghold is formed when deception takes hold in a person's mind. A stronghold is an incorrect thinking pattern that stems from believing something that is not true.
From the very beginning, Satan deceived Eve into believing that God's Word was not true. In Genesis 3:4, the devil told her that she will not surely die as God said she would in Genesis 2:17.
We have two weapons to deal with deceptions: the belt of truth (Ephesians 6:14) and the sword of the Spirit (Ephesians 6:17) which is the Word of God. Both are truth, which is found in God's Word, so why are they given two different names (a sword and a belt)? Because one is meant to be defensive (the belt), while the other is meant to be offensive (the sword). This means that the Word of God is both an offensive and a defensive weapon. A belt is something you wear to guard against an attack, while a sword is used to slaughter the enemy.
You use the belt of truth (God's Word) to guard against the enemy's deception (lies) he sends your way, while you use the sword of the Spirit (also God's Word) to tear down existing strongholds (deception that took hold) in your mind.
In Romans 12:2, we are told to "be not conformed to this world: but be ye transformed by the renewing of your mind." How do we renew our minds? By getting in God's Word! In Ephesians 5:26, this process is referred to as washing of water by the Word: "That he might sanctify and cleanse it with the washing of water by the word."