The original sin is trying to get back up into God. The incarnation is outside of me, not speaking softly in my ear inside my heart yet. But we're talking about history. There were eyewitnesses. If the apostles thought testimony meant talking about Jesus, not themselves, then surely we who weren't eyewitnesses and didn't experience walking around with Jesus on the shore of Galilee should rest in that testimony. It's objective announcement of what God has done for us in Christ.