Who built the Nave of St. Mary's Belchamp Walter?
The Nave of St. Mary's is thought to have been built in the 14th Century. The Nave was built on the West side of the exisiting chapel. When the Nave was built the chapel probably became what is now the Chancel.
The West wall of the original chapel may or may not have had a doorway but the opening that is the Chancel Arch was formed at this time.
The Chancel arch was remodeled in the "renovations" of the Nineteenth Century so it is not known what the form of the original arch was or if there was actually an arch as we see it today. However, there was likely a Rood Screen and Loft, there are still the remains of the entry to that Loft seen on the South wall next to the pulpit.
Who was the "sponsor" for the building and extension of St. Mary's?
This is not known as it was never documented and therefore is subject to speculation.
The nature of the crudity of the wall paintings gives us a clue as the only people that could read and write didn't need to have the holy story explained to them. As they were the ones that were paying for it. The paintings were for those could not read and needed to be told the "holy" stories in pictures.
The removal of the Rood Screen and Loft
It is possible that this occured in the Reformation, as many were at this time.
It is speculated that this was at the same time as the Chantry was removed. My guess on this date was 1574, as this date is carved into the chapel arch.