In the spring of 1966 The Irish Times published a photograph of the Taoiseach, Sean Lemass, in an unusually pensive mode. It was close to the anniversary of the Easter Rising, and - although no one knew it except Lemass himself - he was only months away from his own retirement. In the photograph he is standing at the graveside of Joe McGrath, and McGrath's death must have prompted a more than usually sombre set of reflections. McGrath was his former comrade in arms. He had been his OC when they were interned at Ballykinlar, Co Down, during the War of Independence. They were sundered by the Civil War, at the end of which the security forces, reputedly under McGrath's direction, were responsible for Lemass's older brother's abduction and death.

A decade or so later, an awkward handshake at a race meeting buried the hatchet. McGrath was to become one of Fianna Fail's major financial backers (he also supported other parties), and his death, certainly for Lemass, signalled the end of an era, just as it must have re-awakened the embers of long-banked fires.

But did it signal the beginning of anything else - of an after-life, for instance? The little we know about Lemass's opinions on such matters suggests strongly that his view of organised religion was coloured, as for many of his generation, by the bitter experience of episcopal condemnation during the Civil War. Even before then, contemporaries in Ballykinlar recalled him as a non-conformist and non-worshipper, whose attitude to the pieties of some of his comrades was, at the very least, tinged with irony.

The contrast with de Valera could hardly be more marked. The Chief was a man of unswerving and public orthodoxy, for whom the Catholic faith seemed to have been an extraordinary bulwark (insofar as he ever needed such a thing) against doubt and despair. Lemass's innermost feelings, on this as on many other matters, were rarely revealed except at moments of crisis or loss. The death of an old friend prompted the bleak reflection: "When it's over, it's over."

In the Dail, the only political jibes which got under his skin were those which reminded him of the deaths of friends in the Civil War. For someone who had seen so many of his comrades die as young men, their promise unfulfilled, their energies almost untapped, death must often have appeared in the guise of a horrible finality.

During the second World War, the decisions to execute republicans plunged him into a quietude which could not be explained solely by the demands of collective cabinet responsibility.

On the evidence available, it seems clear that Lemass was, for at least part of his life, an agnostic. What this actually meant for him and in his time is another matter. In this State of ours, in which - if the opinion polls are to be believed - 9 per cent of atheists believe in the Devil, nothing should surprise us. Certainly the idea that in 1959 the Taoiseach of the day was less than orthodox in his religious beliefs would have been a matter of considerable private, if not public, comment.

The public face was impeccable. Indeed, there were occasions when he hewed to the prevailing orthodoxy with some gusto, as during the Patrician Year ceremonies, when he delivered an uncompromisingly Catholic definition of the Patrician tradition (penned in the Department of External Affairs). No Taoiseach would deliver such a speech today, but in the prevailing religious climate it evoked nothing but rapture. Unusually for him, the draft of this speech was amended in only a few minor particulars by Lemass himself before he delivered it.

Whether this was a sign that he agreed with its contents, or simply trusted the fine minds in that Department on issues in which he was not really interested, is difficult to say.

He also paid regular visits as Taoiseach to Archbishop's House in Drumcondra, Dublin, where he took the temperature of the metropolis from the priests of the deanery. Archbishop McQuaid, in turn, probed delicately into the secular realpolitik of which his guest was such an adept practitioner.

But these visits were not about piety, but about power, and the politics of information. It is not so long since Archbishop Desmond Connell lamented, obliquely, the passing of this tradition of discreet political interchange between Church and State.

It is indisputable that Lemass was, as a public figure, a regular Mass-goer and indeed also a communicant. But his practice was also non-showy, and a very private thing. Christmas Eve saw him slipping, almost unnoticed, into midnight Mass in a convent in Leeson Street. Guards of honour and ecclesiastical razzmatazz were foreign to his spirit, wherever it found solace.

At the end of the day, the way in which he left this life was dignified, restrained, and unafraid. If he prayed, his final prayer might well have been that of many before and after him: "Lord, I believe; help thou my unbelief".

John Horgan is the author of a new book, Sean Lemass, The Enigmatic Patriot