We're going to struggle in life. We're going to have problems. We're going to be attacked by Satan. Genesis 3:15 says that Satan will strike our heels, but we will "crush his head." So he's going to attack us and then we're going to stomp him.
We live in a fallen world, but Jesus gives every Christian the authority to use his power to overcome that adversity. Jesus told his disciples, in this world, you'll have trouble, but take heart, I have overcome the world. John 16:33 he also said, all authority in heaven and on earth has been given to me.
Therefore go and make disciples of all nations. This is Matthew 28, verses 18 and 19. The clear implication is that we are to go in his authority