What exactly does it mean to be under authority? And what does it mean to be in authority? To be under authority means "to be subject to". The word "authority" in the Greek is "exousia" (pronounced ex-oo-see'-ah), which means "jurisdiction, power, strength". The Greek word for "under" is "hupo", and it means "placed beneath, literally in an inferior position". So, to be under authority means "to be placed in an inferior position to the one empowered with strength and jurisdiction, to the one in authority over you". In the military it means you are subject to the lawful orders of those who hold a higher rank than you do.
We read throughout the Word of God, how Jesus spoke as one having great authority. Jesus said He came to do the will of His Father. He also came in the power and authority of His Father. If I give someone power of attorney to sign documents on my behalf or to speak as my representative, then, when they sign a document, it carries the same legal stature as if I signed it myself. If they speak on my behalf, they are speaking with my authority. It is as if I myself am speaking. Now, giving someone my power of attorney does not lessen my power and authority. They have the right to use my power and authority, however it is still fully my power and authority. It is not lessened. When Jesus said, "...all power is given unto Me in heaven and in earth" (Matthew 28:18), this did not mean that the Father in heaven no longer had power. When we are given power and authority, it is like a power of attorney. We have the right to use the name of Jesus to heal the sick, raise the dead, cast out demons, etc., but Jesus is still in power.
Let's look at the scriptures to see the order of power and authority, and how it applies to us as believers. First, as we just read in Matthew 28:18 "And Jesus came and spake unto them, saying, All power is given unto me in heaven and earth." Next we read in Luke 9, "Then He called His twelve disciples together, and gave them power and authority over all devils, and to cure diseases." "Behold, I give unto you power to tread on serpents and scorpions, and over all power of the enemy: and nothing shall by means hurt you" (Luke 10:19). In Acts 1:8 we read, "But ye shall receive power, after the Holy Ghost is come upon you..." The passages we have just read are referring to the apostles and the early church. Does the same power and authority apply to the believers of today? You better believe it! Look at Mark 16:16-18. "He that believeth and is baptized shall be saved; but he that believeth not shall be damned." Vs.17, "And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues;" Vs.18, "They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover" (emphasis mine).
Who did God give His authority to? Jesus. Who did Jesus give His authority to? All who believe on His name. That's you and me. Now, if ALL power and authority was given to Jesus, then the only power and authority operating on the earth is what He has given. Jesus is "...the head of all principalities and powers" (Colossians 2:10), because "..having spoiled principalities and powers, He made a shew of them openly, triumphing over them in it" (emphasis mine).
Everything we have talked about to this point has been to establish the foundation for our authority. How do we fit in? God has authority over Jesus. Jesus has authority over all of heaven and earth (which includes all believers). And we, the believers, have power and authority over all devils (this includes the king of devils, Satan). Who then does Satan have authority over? Not you and me, that's for sure! He has authority over his demon followers and over un-believers. When we command Satan and his followers in the name of Jesus, they are subject to and must obey us. Picture this if you will. We confront Satan. When he looks at us, he sees us in uniforms colored crimson by the blood of the Lamb, and he sees us standing in the shadow of the Almighty. If you understand the authority placed in you as believers, you will boldly attack the kingdom of darkness and show no mercy!
"...the kingdom of Heaven suffers violence, and the violent take it by force." Matthew 11:12