Clue: East End theologian's kind of a sponge (5)
Answer: LOOFA
Explanation: Definition: kind of a sponge
For once, the East Ender does not just drop an H, but mangles Luther. Then, of course, there is the definition: is a loofa (or loofah or luffa) well defined as a kind of sponge? This has been argued before in these hallowed grounds, and there is at least some justification – Chambers, for a start, gives "used as a rough, hard sponge".