He [Jesus] called the twelve together, and gave them power and authority over all the demons
Jesus gave His disciples both authority and power over demons. What's the difference? Authority is the right to rule; it's a positional issue. A policeman has the right to stop traffic at an intersection because of the position of authority represented by his badge. Similarly, Jesus gave His disciples His badge to carry. They had the right to rule over the demons because of their position as followers of the One to whom all authority in heaven and on earth has been given (Matthew 28:18).
In contrast, power is the ability to rule. A policeman may have the authority to stop traffic, but he doesn't have the physical ability to do so. If he tries to stop traffic by his own power, he will probably get run over. However, if you move a 20-foot-square cement block into the middle of the intersection, it may not have any authority to make cars stop, but it certainly has the ability to do so!
No good manager would delegate responsibility to his underlings without also delegating authority to them and equipping them with the ability to get the job done. Jesus charged His disciples with the responsibility to proclaim the kingdom of God. Had He not also given them authority and power in the spirit world, the demons would have just scoffed at their feeble attempts and sent them running for cover (as they did the seven sons of Sceva in Acts 19).
The truth is that, while in yourself you don't have the ability to resist Satan and his demons, in Christ you do . The Israelites looked at Goliath fearfully and said, "We can't fight him." But young David looked at Goliath and said, "Who is this uncircumcised Philistine, that he should taunt the armies of the living God?" (1 Samuel 17:26). The army saw Goliath in relation to themselves and trembled; David saw Goliath in relation to God and triumphed. When you encounter the spiritual enemies of your soul, remember: "Be strong in the Lord [your authority], and in the strength of His might [your power]" (Ephesians 6:10).
Prayer: Thank You, Father, for Your authority and power. Help me view my circumstances in light of what You can do, not according to what I can't do.