A couple of excerpts from the excellent book The Trellis and the Vine on the centrality of the gospel:
“Throughout the world, the gospel is spreading, propagating, budding, flowering, bearing fruit. People hear it and by God’s mercy respond and are saved. But it does not stop there. Once the gospel is planted in someone’s life and takes root, it keeps growing in them. Their lives bear fruit. They grow in love and godliness and knowledge and spiritual wisdom, so that they walk in a manner worthy of their calling, fully pleasing to the Father, bearing fruit in every good work (Col. 1:9-10; 2:6-7)” (36-37). [emphasis mine]
“The New Testament envisages that all Christian disciples will be prayerful speakers of God’s word, in a multitude of different ways and contexts. In each context, the message is essentially the same. It’s not as if we come to know Christ through the gospel word but then use a fundamentally different message to encourage each other as Christians. The ‘word of God’, the message that he has revealed in and through Christ by his Spirit–this is what converts us, and it is also what causes us to grow, bearing the fruit of godliness. The vine grows, both in number and in leaves and in their quality and maturity, through the word and Spirit–through God’s truth being heard, and the Spirit making it effective in people’s hearts” (53-54).