I had arranged to see Bill Viola’s big retrospective exhibition at the Palazzo Strozzi well before he was elected an Honorary RA, having been an admirer of his work ever since seeing The Messenger in the nave of Durham Cathedral in 1996, the date of The Crossing, the first work in his current exhibition (he also has exhibitions in Hamburg and Bilbao).   The Crossing is a powerful introduction:  stripped back to the essentials of the desert and pillar of fire.   Next door is The Greeting, shown alongside Pontormo’s Visitation, borrowed from Carmignano, a tough double act which demonstrates, if it’s necessary, how much his work is imbued with Renaissance imagery.   I liked The Four Hands (2001), a very simple, black-and-white work about the expressive power of hands – fingers clasped, touching and in prayer.   Then you come across Uccello’s Flood  and the effect is that you very much want it to move.   Viola certainly knows how to use the sacramental qualities of slow-moving film to powerful visual effect and is not at all afraid of – in fact embraces – traditional biblical imagery with its layers of history and meaning.