Much of the greatest art of the Western world is religious, but with the age of modernity the decline in religious art reflects the erosion of faith and of church authority, influence and, arguably, intellectual vigour. Where during the Italian Renaissance Pope Julius II commissioned Michelangelo and enjoyed a close and tempestuous relationship with him, the Vatican's record of patronage in the 20th century is lamentable, and with some honourable exceptions the art it has favoured veers towards kitsch.

It's hard not to read a failure of nerve into this retreat, and it applies in Ireland as elsewhere. Here, it should be said, church decoration has been an important if peripheral strand of artistic practice throughout the century, involving some outstanding individuals, including Harry Clarke and Mainie Jellet, as well as many adequate if unexciting talents. The fact is that the vast majority of overtly religious art is an aesthetically tame, decorative play on devotional themes, much of it positively insipid. The background to Hughie O'Donoghue's exhibition, Episodes from the Passion, at the RHA Gallagher Gallery, is well aired by now. While visiting Florentine churches together and discussing their shared love for Italian art, American businessman Craig Baker and O'Donoghue entered into an extraordinary patronage agreement. The former would fund the creation of a series of works based on what had been, until relatively recently, a staple theme in Western art, the Passion of Christ.

That was in 1986. It is clear that O'Donoghue attacked the commission with incredible zeal and dedication. After a long process of rejection and revision he showed a large body of work under the title Via Crucis at the Haus der Kunst in Munich in 1997. The works in Episodes from the Passion are a major part of what he has produced to date, and they are now on long-term loan to the Irish State. The paintings and drawings have huge physical presence. They are enormous, imposing images, and they look wonderful in the RHA Gallagher Gallery. In fact, uniquely for this exceptionally capacious venue, the two smaller galleries seem dramatically diminished in size. Yet the pictures are not gratuitously or bombastically large. They really do earn their scale. Some of them are virtually abstract, presenting us with sombre expanses of subdued, grey-toned earth colours, illuminated by a fiery, ethereal glow. In others, disconcertingly, we chance upon almost photographic details lodged in the vast expanses of dark earths: a fragment of a face, eerily lifelike. O'Donoghue has previously made paintings inspired by the discovery of bodies preserved in bogland for thousands of years, and many of the bodies in the Passion images seem similarly disinterred. It is as if they nestle into the accommodating paint surface. Buckled, susceptible creatures, they are very much of the earth. One can't help feeling that with a bit of imaginative flair the Church, rather than Craig Baker, might have commissioned this contemporary take on the Passion. Not necessarily these precise paintings, perhaps, but if not them, then their equivalent. But O'Donoghue is anything but a tame, decorative craftsman.

All the evidence demonstrates that he is not remotely interested in manufacturing variations of platitudinous religious iconography. Rather his interest is in cutting to the core of the issues raised by religious belief. Can we transcend the boundaries of our physical existence? Does religious faith provide the spiritual framework that makes that possible? What is the nature of Christ's sacrificial gesture? These are basic questions given our predicament as conscious creatures in the world. Perhaps the secular source of the commission simply accords with the fact that artists who have asked real spiritual questions this century, such as Mark Rothko, came upon the issues out of personal necessity and usually seem remote from the trappings of institutional religion.

hen you look at these monumental paintings and drawings it is striking that there is nothing grandiose about them. On the contrary, in the best Christian tradition, they are marked by a real humility. The figure at the heart of the works is an everyman, open to the world, a receptive presence, beaten, scourged, crucified. There is no glorification of sacrifice here. It seems to me that the emphasis is on incarnation: the experience of being a living person faced with the inevitability of death and trying to figure out your position in the scheme of things. In the end they do not answer any questions. On the contrary they put questions to us, prompting us to reflect on our own experience. They are concerned with active spiritual struggle, rather than its ossification into religious dogma. They do not trumpet the exclusive truth of the religious narrative to which they refer. Their implication is rather that, if religion has meaning, any meaning at all in our lives, then it must start here, in the facts of our lives, and on the basis of faith: faith, in the first instance, in the capacity of art to embody the truth of our earthly existence.

Episodes from the Passion by Hughie O'Donoghue continues at the RHA Gallagher Gallery until February 22nd.