In Ephesians 6:11-18, the Apostle Paul talks about "putting on the whole armor of God".
In verse 15, he says that God's Peace is under your feet. When you put on your shoes of Peace, your feet are shod with the preparation of the Gospel of Peace. The devil is to be kept under our feet ... our feet of Peace.
Jesus goes on to say in verse 19 of Luke 10 that "nothing will harm you".
In verse 20, He says, "Do not rejoice that the spirits are subject to you, but instead rejoice because your names are written in Heaven". At this time no one was born again so their names were not written in Heaven. The New Covenant had not been established yet. Jesus was speaking prophetically here.
Reverend Robert W. & Mary C. Butler