Humans have long perceived the existence of both a physical world and a spiritual world. Even the early Greek philosophers held to this belief. In all truth, the physical world is not all there is in this universe. There exists the presence of two spiritual powers. One is God's and the other is the evil darkness of Satan's kingdom. God delivers people into His kingdom, but Satan's army tries to takes them by force. So how can you be saved from this wicked generation (Acts 2:40)?
How did Joshua defeat Amalek? The Bible records that he did so "with the edge of the sword." This kind of action requires courage and strength. It also demands of the warrior a sense of ruthlessness. The swift action of each blow is decisive—there is no time to hesitate. The whole person must lean into every strike, as he strikes one enemy after another until there are no more to defeat. Not one must live; not one must have the chance to approach his heart and pierce it with his sword. Joshua and the Israelites fought the Amalekites with their lives at stake.
The same mindset applies in the spiritual realm and the battle we face. The spiritual battleground is your heart, for Satan does not want anything other than your heart. If you fail to resist him in time, then it belongs to him. Once your defenses have been compromised, the enemy is one up on your life. Partially open gates and unrepaired walls are points of entry through which Satan can gain access to its throne. And when the forces of darkness gain free access into your heart, God will depart. Like Judas, as soon as we surrender to Satan and his ways, we will have lost.
Having a sharp sword will not save us; using the word of God, "sharper than any double-edged sword" (Heb 4:12), as our defense will. Unfortunately, Adam and Eve did not guard their hearts, and the serpent threw in a seed that began to grow. Their desire was too strong for them to resist. Instead of striking while they could, they gave in and consequently lost their true freedom. Guard your heart with vigilance, and with fortitude—for if you give way, you give up the wellspring of your life (Prov 4:23).