Found in the FAA request records,
Structure Type: Building Structure Name: Fort Worth- First Christian - NO FREQUENCIE
So, something up to 100 feet. The coordinates are about right on the parking lot to the north.
I've looked in a few other places to see if I could find any other info (past few church newsletters, zoning permits, DDRB records, etc) but didn't find anything.
I suspect First Christian is riding the wave that the next door Frost Tower is bringing to that part of town, and perhaps anticipating the future Sundance hotel on the block to the NE, maybe they are planning an office or residential building rather than an actual expansion of the existing church? A parking garage for church goers perhaps (wouldnt really be a building though)? Not much else to go on here.
Other thing I wonder about is how a large high rise type building might affect the historical integrity and setting of the existing church itself. A large building could be overwhelming, however the block is surrounded on all sides by high rises and skyscrapers already.