When Jesus died on the cross, the devil thought, 'Now I am soon the king of the earth!' But a 'It is finished!' from Jesus disarmed him completely. 

'Having disarmed principalities and powers, He made a public spectacle of them, triumphing over them in it.'

Col. 2:15 

In the invisible, spiritual world, there was a battle that was won by Jesus. God had received full payment for all our sins and illnesses (which were the result of the fall). Satan now had lost his grip on humanity, for all sin was now paid for by Jesus' atoning death. 

Who wants to be confronted with a colossal blunder and a great loss? Certainly not the devil! Remind him of the cross – and he will sheepishly leave you.

'And they overcame him by the blood of the Lamb and by the word of their testimony.'

Rev. 12:11 

Don't forget: You are on the winning team, Satan has lost and he knows it, for it is written in black and white in Revelation 20:10:

'The devil, who deceived them, was cast into the lake of fire and brimstone where the beast and the false prophet are. And they will be tormented day and night forever and ever.'

However, concerning the believers, it is written:

'And I heard a loud voice from heaven saying, "Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people. God Himself will be with them and be their God."'

Rev. 21:3