1 Thessalonians 1:5
For our gospel came not unto you in word only, but also in power, and in the Holy Ghost, and in much assurance; as ye know what manner of men we were among you for your sake.
When you preach, don't just preach, demonstrate the Word. Heal the sick, cast out devils. See 1 Corinthians 2:4.
This is what it means when you say the Word of God came with power. Matthew 10:6-8 says But go rather to the lost sheep of the house of Israel. And as ye go, preach, saying, The kingdom of heaven is at hand. Heal the sick, cleanse the lepers, raise the dead, cast out devils: freely ye have received, freely give.
These are the hallmarks of a believer (See Mark 16:17-18).
