The same way that law enforcement has the authority to enforce the law (literally in their title), we've been given authority to enforce the Word of God over all the works of the enemy (Matthew 28:18).
Satan may be the god of this world, be he and all of his demons are subject to the Word of God. The enemy cannot stand against or resist the authority that Yeshua has given us.
The authority given to us is not based on whether we are good enough or whether we feel worthy to walk in that authority. It's based who we are in Christ. Just as the badge of a police officer represents the authority in the natural, the Blood of Christ is our badge in the Spirit.