First, the problem is disruption of the Eikon of God in its union with God, in its communion with others, with manifold implications spilling over in all directions, including its relationship with the rest of the created order.
Second, the solution is reconciliation: with God, with others, and with the rest of creation. A good word for this is Shalom, and it needs to be understood eschatologically or teleologically: to know what the gospel is all about we have to know what God wants to do with the world he has created and where the world is going. Let me put this differently: the solution is the Kingdom of God as Jesus envisions it and as Jesus embodies it and as Jesus teaches it. As I explain in the Jesus Creed (chps. 13-18), that kingdom is a society in which the Jesus Creed/Will of God is done. That was the goal of Jesus' ministry: the Kingdom of God.
Third, the means of that solution, as the 4SL has it, is Jesus Christ. But, Jesus Christ must be seen as a person within the Trinity: so the solution is the Father/Son/Spirit's work in restoring us, through three "acts of God," none of which can be minimized without damaging the gospel: Cross, Resurrection, and Pentecost. The means, in other words, is a Person (triune one) and to know that resolution means to come to know God personally.Fourth, the context of that resolution is the people of God: anticipated in Israel and finding its Christian completion in the Church. The Church embodies the gospel, and the Church does so through Word, sacrament, and performance of that gospel in faith and obedience. Which means this: the gospel is encountered through an advocate (if you want to read up on conversion theory, read this). The most potent advocate is the Church itself, but the Church finds individual embodiment in the individual Christian who is the typical form of an advocate. (Others could be mentioned: the Bible, TV, Christian art, etc.). Which means this: the gospel cannot be separated from the Church, and the goal of the gospel is to restore Eikons so they live in union with God, in communion with others, in the context of the Church, for the good of the world.