It's going to be a busy day, Trinity Sunday 2013: I have an 8am communion (short sermon - usually a 'filletted' version of a later one), 9.30 communion, 11.15 all-age service, a baptism at 12.30, and then "beer and hymns" at the local pub in the evening.
I think my starting point is going to be Psalm 8: which speaks of the glory and wonder of God - but also of God's mindfulness for humanity - a God who is at once transcendent and immanent. Somehow we need to hold onto the idea of God as both immense and near to us and in us: perhaps one way of handling the idea of God as Trinity is to try to similarly hold onto God as over all, and with all, and in all.
Only God in Trinity can make sense of what Jesus says in John 16: 12-15 of the coming of the Spirit
'All that the Father has is mine. For this reason I said that he (the Spirit) will take what is mine and declare it to you.'.
The phrase 'all that the father has is mine' implies complete indwelling - otherwise it makes no sense. I might say 'all that I have is mine' - but I could not say that all that someone else has is mine, unless we are one: even then, in a human sense I would say 'all that we have is ours'...
Trinity Sunday - busy AND thought-provoking... more to follow!