What is the use or the significance of the ornamental gold cross in Castlevania: Order of Ecclesia?

Solution 1:

As far as I know, the only thing to do is to destroy the lower portion of the wall, as it conceals a hermit ring.

Here's a youtube video of someone breaking the wall:

Solution 2:

Actually, a later quest with the old lady has you sketch the inside of the church, so the cross sseems to act as a marker for that.