Faith began with the story of Abraham in Genesis 12; it did not begin with Jesus or Paul. At the foundation of the economy of salvation lies the grace of God. God called Abraham out of nowhere. He was nobody when he was called and did not deserve anything. Abraham's part was his faith—acknowledging and accepting God's blessing and call through trust, which was a lifelong commitment. Jesus showed this same kind of faithfulness as the Son of God when he demonstrated God's righteousness to the world (Romans 3:22). He came not to destroy the law or the prophets, but to fulfill them (Matt 5:17). He argued that God loves all; therefore, all people need faith.
Likewise, the "good news" began with God and the story of Abraham. God started a new story and history with him. Thus, the good news of God is paramount. The first thing Jesus proclaimed was the good news of God (Mark 1:14). Similarly, Paul stated that his calling as an apostle was set apart for the good news of God (Romans 1:1).
In Galatians, Paul affirms that the root of the gospel is in God. It is not ultimately in Jesus or Paul, but in God himself.