Ephesians 6:11
“Put on the whole armour of God, that you may be able to stand against the schemes of the devil.”

Satan is essentially on a leash. Nothing he does is without God allowing it. God oversees every step the devil takes.

William Gurnall was a 17th century Christian pastor who authored “The Christian in Complete Armour”. His famous works noted the three following points about Satan’s power:

1) Satan’s power is a derived power
God created Satan, and any power he has is because God has given it to him. 

2) Satan’s power is a limited power
There are limitations and he can only do what God allows him to do. Satan can’t do anything without the approval of God.

3) Satan’s power is a ministering power
Ultimately, Satan’s schemes serve for the benefit of Christians. God uses the devil’s tactics to remove our flaws and sins as if they were specs of dirt on a white sheet. 

“Satan seeks to ruin our graces and destroy our souls, but God’s thoughts are comfort and peace”

– William Gurnall