Here is a neat Early Church example of the Trinity as Gospel. The writer of the Epistle to Diognetus demonstrates that Christ reveals to us God’s nature as the foundation of our salvation. What was hidden before – the true relationship of God to the world and therefore his character – is revealed through Christ, giving us understanding of God, creation, ourselves and making salvation available to us:
“He always was was, and still is, and will ever be kind and good and free from anger and true; and he formed in his mind a great and unspeakable plan which he communicated to his Son alone. As long, then, as he held and preserved his own wise counsel in concealment he appeared to neglect us, and to have no concern or care for us. But after he revealed and laid open, through his beloved son, the things which had been prepared from the beginning, he conferred every blessing all at once upon us, so that we should both share in his benefits and see and understand”
Epistle to Diognetus, Chapter 8, Quoted in Michael Green, Evangelism in the Early Church , Hodder & Staughton:London, 1970, (134).