Most ministers I know avoid Trinity Sunday like a plague of Egyptian locusts. A couple of years back I decided it was time to stop the avoidance and engage with the challenge; for the most part people seem to appreciated it. One of the challenges, irrespective of the age of your congregation, is finding suitable illustrations, well, assuming of course you want to go that way of course. Many of those I found on a quick web trawl are familiar - the shamrock leaf, the three states of water, the dreaded trifle (which I'd never heard of until I began training as a minister and its badness has stuck firmly in my brain) and this time I found eggs, apples and even jaffa cakes! The problem with these images is that they slip into modalism - three modes or functions of God - three people rather than the three personae. Trouble is, the more theologically orthodox concepts are utterly impossible to explain or illustrate, which is why I suspect we live with the modalism.
Evidently St Patrick held up his shamrock/clover leaf and said "is it three-in-one or one-in-three?" His hearers allegedly said 'both,' which is about as good, and non-modal, as you're going to get.
So, I'm back to mulling over what I'll do for the "all together" part of our service and thinking the shamrock is a pretty good contender, all things considered. Perhaps we over-rationalise mystery, perhaps we stetch metaphors to breaking point, and perhaps we're either too fearful or too ignorant of heresy to find creative means of exploring the wonder of a triune God?