“Yet it was not I, but God Who was working through me by His Grace. So it makes no difference whether I preach or they (the other apostles) preach, for we all preach the same message you have already believed.” 1 Corinthians 15:11 NLT.
When God is at work sending forth His Good News, it does not matter who the preacher is; the powerful, life-saving Gospel is reaching sinners, who can enter into saving faith in Jesus Christ.
Over nearly 2000 years, the Good News of Jesus Christ has been preached in countless lands by countless evangelists; but when God is at work in the speaker, the message is always the same. Jesus Christ died for our sins as the scripture foretold. He was raised again on the third day, as the scripture foretold. Those who believe in Him, and continue to put their faith in Him, will be saved.
This does not mean, of course, that every person who “preaches” is motivated and directed by God. From the days of the early church, false doctrines have been taught, instigated by God’s Enemy and spread by those who were deceived. God Himself, by His Holy Spirit and His written Word is our only safeguard against falsehood; those who wholeheartedly seek Him and His Truth will find Him completely trustworthy to keep them in the Truth.