1 Thessalonians 1:5 (KJV) 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.
Words are innately powerful. Combine that with the Holy Spirit, the power becomes infinitely multiplied (really hard to come up with the appropriate description because each of them is already infinite in their power). Most probably, the context refers to a manifested and/or demonstrated and/or visible power. Imagine the effectiveness and the credibility of a ministry that possesses both.
And even more, we have genuine lives—messengers who are full of integrity. This shows us why a ministry becomes unquestionably effective, efficient, and expansive. These three powerful factors working together as we serve each other and reach out to the needy and “hopeless” is much better than missing even one of them. God loves us greatly as His children that we are lavishly graced with all of them. God loves those who we serve greatly that He wants them to have undeniable proofs of His reality so that they would turn to Him and also live the best life anyone can ever live—the life of a believer.