The OT built the foundation and steps, the NT finsihed the walls and roof, and SOP furnished the house.
The OT and NT built it all and furnished it all. Nothing can be improved on this house. SOP might be akin to the guest house by the pool that was built a little later.
I would be more inclined to see the SOP as a member of the household who points out certain critical details in the structure that have been overlooked or neglected over the years. There is no change or improvement in the house itself (since what God builds needs no improvement), but, thanks to the SOP, there is appreciation and understanding of various aspects of the building that have been obscured by the cobwebs of time and tradition. Some of these details help fill in some of the blanks that have puzzled us over the years, while some of the details are vital to the survival of the residents.
Since this topic is that somewhere in the 4 gospels - every doctrine is either taught or alluded to. Somebody pick a doctrine not normally associated with the 4 gospels and every start the Biblical treasure hunt. Then post. Jesus had things he liked to talk about and they get repeated over and over in the gospels . Somebody pick one.