Power and authority is given to us by the grace of God to carry on the commission of God to take his word out into the world for the hope of others as Gods Spirit draws them into his salvation. This power gives us victory over the wicked forces of Satan and his dominions that are in the world trying to defeat us in our quest for the Lord if we take authority over him in the name of Jesus. There is no reason we have to fight Satan for God has already given us the victory over him in our life and if we fight him in the flesh he will mock us and destroy us. Authority is what gives us the power to teach the doctrines of Christ no matter what other teachings comes against his word as we are Gods influence in the world as his Spirit works in us and through us to let that light of Christ shine out to the world. Never worry about the persecutions of this world as we might have to live in it, but are no longer a part of it and we must be about our Fathers business in all things.
There are fourteen definitions of the word authority listed below found in the Strong's Exhausted Concordance in the Greek Dictionary. I have listed each definition with scripture to show you the strengths we do have by taking action on Gods word to unleash the Holy Spirit in our own life to be an effective servant to those who need Jesus in their lives to bring that faith that is Jesus which is the life changing promise of Gods word.
Greek definition: (exousia, ex-oo-see'-ah) freedom, influence, delegate, jurisdiction, ability, control, force, privilege, strength, liberty, mastery, competency, power and right
I could give all the definitions with scripture, but would have to do that within three different post. But you can take each definition and look them up in scripture.