“The Gospel of God "is the" word of God" (see v.13). The Christian Gospel is not "just one religion among many"; it is from God. The Gospel is the "good news" of God to the world, announced by messengers accredited by Him. In this passage, Paul speaks of his experience in Thessalonica - and the lies of his enemies, who accused him of various false motives.
After having “suffered and been spitefully treated" at Philippi (Acts 16:9-26), the preachers (Paul and Silas) also had “much conflict" in Thessalonica (see Acts 17:5). However, there had been conversions, and for many, the Gospel was received as a message from God (v.13). The lives of the believers glorified God, for the Gospel "worked effectively "in them.
Paul was not like those in 2 Timothy 3:13. In him there was no mixture of immorality, as in many pagan religions (and Mormonism) nor cunning of words and methods, such as spiritualism, "Jehovah's Witnesses" and several modern sects. God gave Paul the message and he taught the truth of God, without asking for favours or money from others.
Watch out! There are preachers who "facilitate" conversions: their message is weak and they do not insist on repentance, or the abandonment of sin. But Jesus Christ must be LORD in the believer's life.
The Gospel is not to "believe only" - at least, not in the sense commonly understood by that phrase: that is, that a sinner, once believing the Message is from God and then the truth about the life, death and resurrection of Christ and confessing publicly this conviction, is therefore saved, without the need to turn from sin and to make of Christ, in practice, the true LORD of his life. In other words, the teaching of "believe only" undoes the need for repentance as the basis of saving faith. See Acts 2:38, 26:20, Ephesians 2:8-10, James 2:14-26.
Paul did not seek the praise of men, not even of believers!
The preacher must be an example of Christian life. The believers in Thessalonica could testify about the procedure of Paul. For those new Christians, he was a "model", a true "father in the faith" ... His honesty and sincerity, his sacrificial love - everything was clear to them. He did not ask them for money, he did not live regaling himself among them; he sacrificed himself in many ways, to guide them in the Christian life. In the procedure and character of Paul the Thessalonians saw something of the Lord and Saviour that he proclaimed to them.
So should be every preacher of the Gospel. So glorify our Father, as His children.
1 For you yourselves know, brethren, that our coming to you 2 But even after we had suffered before and were spitefully treated at Philippi, as you know, we were bold in our God to speak to you the gospel of God in much conflict.
3 For our exhortation did not come from error or uncleanness, nor was it in deceit.
4 But as we have been approved by God to be entrusted with the gospel, even so we speak, not as pleasing men, but God who tests our hearts.
5 For neither at any time did we use flattering words, as you know, nor a cloak for covetousness—God is witness.
6 Nor did we seek glory from men, either from you or from others, when we might have made demands as apostles of Christ.
7 But we were gentle among you, just as a nursing mother cherishes her own children.
8 So, affectionately longing for you, we were well pleased to impart to you not only the gospel of God, but also our own lives, because you had become dear to us.
9 For you remember, brethren, our labor and toil; for laboring night and day, that we might not be a burden to any of you, we preached to you the gospel of God.
10 You are witnesses, and God also, how devoutly and justly and blamelessly we behaved ourselves among you who believe;
11 as you know how we exhorted, and comforted, and charged every one of you, as a father does his own children,
12 that you would walk worthy of God who calls you into His own kingdom and glory.
1 Thessalonians chapter 2, verses 1 to 12