To Lumen
..."our theology is not based solely on Scripture "....

Not 'solely' true enough. But 'Theology' is supposed to be the study and knowledge of "God" and we have claimed that the core of that knowledge is based on 'God's Revelation' as found in the Scriptures -- and then made deductions and reasoning from that original 'core'.

Scripture, in the Gospels, is the only source we have for the knowledge and teaching of Jesus.  The logic that leads to a Church begins with a believe in the very fundaments of Christianity - the death and resurrection of the Lord Jesus Christ for the remission of sin.

That's the Jewish conviction, that God is appeased by sacrifice, that the coming Messiah would suffer and die. 'By his stripes, we are healed', etc.. 

The fact that there was no Adam and Eve to commit and pass on an 'original' sin, shows that Jesus must be redeeming us for our own sins. Jesus is the Savior for each one of us. We each commit our own 'first' and subsequent sins.