"In 1 Thessalonians 1:5 , Paul makes a most important statement in this connection: ‘For our Gospel came not unto you in word only, but also in power, and in the Holy Ghost, and in much assurance.’ Now if you read that epistle, especially the first two chapters, you will find that the Apostle goes on repeating that statement in different ways. He says that they received the word that came to them ‘not as the word of men, but as it is in truth, the word of God’ ( 1 Thess. 2:13 ). But what did he mean when he said ‘For our gospel came not unto you in word only’? It did come in words, of course, the Apostle was speaking, but that was not the thing that had turned those idolatrous Thessalonians into saints. What was it, then? It was that it had come ‘in power, and in the Holy Ghost, and in much assurance’. It is this internal work that turns people from sinners into saints; this is preaching in demonstration of the Spirit and of power." (Dr Martyn Lloyd-Jones)