It is quite timely to be called to meditate upon the Trinity as a third person enters my family. Perhaps this is what prompted a very kind couple from the congregation to bring us a beautiful icon of the Trinity from Greece as a birth gift.
Some may say that two is company, but so far it seems to me that the effects of a third person on the dynamic between an original two can be very positive. Indeed, it can bring out the best of that relationship and open its joy and love to a wider world. Yet other families will know all too well that bringing forth new life is not without its risks.
So it is, I think, with the Holy Spirit and its role in the relationship between the Father and the Son. It is therefore no coincidence that Trinity Sunday follows so closely after Pentecost. For while the Spirit gave inklings of itself long before - such as when it moved over the waters of creation, or overshadowed the Blessed Virgin, or descended like a dove at the Baptism of our Lord - it is only at Pentecost that it is fully and universally revealed. Universally, I say, because as Holy Spirit, God speaks at Pentecost in every tongue to everyone; and fully, because it is the fulfilment of Jesus' promise to send a comforter and counsellor after Him into the world for all time.
St Paul, it is sometimes said, wrestled with the problem of a 'binitarian' God: how can God be both Father and, if Jesus is who He says He is, be Son at the same time? The coming of the Holy Spirit complicates this question further, and the doctrine of the Trinity answers it, albeit haltingly and paradoxically. But it is not just a game of theological mathematics. It is a matter of love, and that brings me back to where I started.
If God were just Father and Son, we would be left with an introspective and impenetrable deity, looking forever at itself as though in a mirror. To extend the simile, the Holy Spirit is the light that passes between the viewer and the reflection, and which also spills out to allow us to join in the vision. It is the overspilling of the love between the Father and Son which pours out into the world and by which the world can be drawn into their intimacy. Such intimacy entails risks, not least the risk of betrayal, but love makes the risk worthwhile. Love makes the Cross worthwhile.
Three is not a crowd. It is an invitation.