No Holy Spirit No Conversion

"We know, brothers loved by God, that you have been chosen, because our gospel came to you not only in words, but also in power and in the Holy Spirit and with great affect." (1 Thessalonians 1: 4-5)

I paraphrase the above scripture thus: Although we used words to convey the message of the gospel, those words were imbued with power by the Holy Spirit. That is why they were very effective in your case.

When we share the gospel with people, the gospel is effective in proportion to the control of the Holy Spirit in the process. The more we let go and let the Holy Spirit, the more effective is our witness. The Holy Spirit is not just the power behind the words, He is the effective cause of conversion. No Holy Spirit, not conversion.