Paul was accused of making up a new religious philosophy or presenting another person’s academic thesis about God – to make money and a name for himself!  But Paul denied that quite emphatically.  Humanly speaking there was no reason for Paul to embrace anything except the Jewish Law, about which he was an expert (Philippians 3:4-6).  However, Paul’s encounter with Jesus Christ on the road to Damascus produced a radical change in his thinking (Acts 9:3-6): instead of persecuting Christians and destroying their churches, he preached to them and prayed for them in the Name of Jesus (Acts 9:20-22).

Why did Paul preach the gospel?  Because he had received it from Jesus (Galatians 1:15-17) and was commissioned to preach it (Acts 26:16-18).  It brought the Old Testament prophecies to life and was powerful to bring sinners to salvation and eternal life (Romans 1:16).  But there were many travelling preachers peddling many philosophies and religious ideas.  Those with charismatic personalities and oratory skills gathered a good audience who paid well for the intellectual entertainment.  But Paul never charged (Acts 20:33-34) and was not a professional religious entertainer (1 Corinthians 2:1-5).  
 
He was just the messenger and Jesus had given him the message.  Subsequently, Jesus taught him many things, allowing Paul to see how the Old Testament Scriptures were looking forward to Christ (2 Corinthians 1:20).  Without Jesus, the Law was incomplete.  That is why Paul preached that Christ was the fulfilment of the Law (Ephesians 1:10).  With the personal words of Jesus, a profound knowledge of the Law and the inspiration of the Holy Spirit, Paul knew that Jesus is the only Saviour.  Three years later, when he met the Apostle Peter, they found that they both had exactly the same understanding of the gospel (Galatians 1:18-24)!
 
The gospel is uniquely God’s.  No human reasoning could invent the idea of God the Creator accepting responsibility for the sins of His people … being willing to be constrained by a human body, to be punished by death, so that sinners might become saints.  The gospel is the announcement of God’s salvation-plan.  He communicated it to the disciples in Jesus' lifetime and later to Paul by special revelation.  Today, although many people proclaim the gospel, it is not theirs but God’s.  When people respond they are simply being obedient to God who is speaking to them through the message.  So whenever you announce Jesus Christ as the Saviour of the world and the friend of sinners, expect God to speak to people and pray that they will respond obediently to God’s revelation of Himself.