Walking into an exhibition of two paintings by a Renaissance master would be surprise enough but to find myself looking into the Garden of Gethsemane shook me about right.

The thing is, I hadn’t really meant to be at the Ulster Museum at all, only at the hot houses nearby in Belfast’s Botanic Gardens and that was because I had started missing Singapore. I just wanted to get in and feel heat and humidity again, look at big waxy flowers and giant leaves – all in a tightly controlled, cramped space of course, for the full Singapore vibe!

As I wandered the hot houses like a hungry ghost I thought back to the hot, scented darkness of evenings spent walking in Singapore’s Botanic Garden or in the roof garden below the tower block where I worked earlier this year. To be in a garden at night with the temperature still barely below 30C was such a novelty for me that I could think only of the Garden of Gethsemane, the place in Jerusalem where Jesus Christ was betrayed according to the Bible. I have no idea how hot it would have been on that actual night nearly 2,000 years ago, but that was the illusion I was quite happy to entertain. In the Palm House on Thursday, I felt such a pang of longing for South-East Asia that I nearly cried.

Coming out into the Botanic Gardens again, into the cool of an Irish summer afternoon, I was heading for the far exit on my way to Belfast city centre when I gave in to an impulse – I was on only the briefest of visits to Northern Ireland – to nip into the museum. It remains one of my favourite treasure-houses, if only for its Spanish Armada exhibit: the wreck of the Girona with its gold from the Americas and rubies from Burma. And what did I find inside but a rare reunion of two Caravaggio paintings which had adorned the same Roman palace four centuries ago: The Supper At Emmaus, on loan from the National Gallery in London, and The Taking Of Christ, on loan from the National Gallery Ireland in Dublin.

I couldn’t look at Emmaus without laughing, politely of course. The subject is two of Christ’s followers who have unwittingly been eating with him in an inn after his death and suddenly realise he is back from the dead and back with them. Presumably they failed to recognise him without his beard! One flings out his arms in amazement while the other clutches his chair. WTF At Emmaus might be a better title.

The Taking Of Christ, on the other hand, terrifies me. It shows the moment after Judas embraces Christ to identify him for the soldiers who will take him away for the ordeal that will end in his crucifixion. Judas greedily clutches Christ’s shoulder, his lips still pouting from the fatal kiss, glazed eyes staring out of flushed face. One soldier has placed a steel-gauntleted hand on the doomed man’s chest. Christ’s eyes are closed, his expression pained but resigned, his fingers locked in prayer, as someone behind him cries wildly for help. It is a devastating depiction of betrayal.

I came away thinking about many of the betrayals in my own life, great and small. Sometimes I’m afraid to shove my hand into my pocket in case I find 30 pieces of silver in there. I also thought of a few points where I had stayed loyal, to people or ideas. Such is the power of great art.