Power is delegated from God Romans 13:1 , Jesus received it from the Father and now has delegated it to believers.This power was evident and was manifested in the Old Testament with miraculous signs and wonders especially in the desert, with Joshua in conquest of Cannan,to Samson to David... This was continued in the new Testament starting with our Lord and the Apostles. Believers were given power overcome Satan and his agents ,Luke 9:1 Jesus give authority to the twelve to cast out demons and heal diseases, he gave authority to the 70 followers in Luke 10:19 . He then gives them the assurance that nothing shall by any means hurt them. We then ask ourselves how and why does it seem this power is no longer at work? The authority is only manifested by those who walk in obedience, in humility and in faith. If any of this is lacking then the power won't be manifested. This power is manifested in weakness 2 Corinthians 12:9. This power resides in us. 2 Corinthians 4:7, Ephesians 3:20, this power is limitless for we can do all things through Christ who strengthens us Philippians 4:13. We have this power ,the same power that raised Christ from the dead and placed him at the right hand of God in the heavenly realms. We are also raised up with Christ by the same power and has seated us with Christ in the right hand of the Father. We ultimately overcome the enemy, infact it's not a contest but a walkover as we fight from a position of victory. You don't just realize how much power you have from God, exercise it in Him .Amen