The devil and his demons hinder the coming of God’s kingdom. He wants to cause the heart of God's people to turn away from Christ’s message. He sees God’s plan, knows that God’s message is coming (with irresistible authority), and he does what he can to make people unwilling to accept it.
1 And he called to him his twelve disciples and gave them authority over unclean spirits, to cast them out, and to heal every disease and every affliction.