Lawrence Osborne in Lapham's Quarterly:
In his introduction to Kim Philby’s My Silent War, published in 1968, Graham Greene laid out the case for betrayal as an understandably human problem that needed, in the end, to be forgiven. Philby, the aristocratic son of the orientalist and Islamic convert H. St. John Philby, served as a high-ranking British intelligence officer and Soviet double agent until his defection to the Soviet Union in 1963. “The end, of course, in his eyes,” Greene wrote of the luckless traitor (who died in Moscow in 1988),
is held to justify the means, but this is a view taken, perhaps less openly, by most men involved in politics, if we are to judge them by their actions, whether the politician be a Disraeli or a Wilson. ‘He betrayed his country’—yes, perhaps he did, but who among us has not committed treason to something or someone more important than a country?
It’s a well-known passage that has been used many times to cast a baleful eye on Greene’s own love affair with communism. Philby, he goes on to observe, possessed the same “chilling certainty” as the Catholics who worked for the Spanish under Elizabeth I. It was the “logical fanaticism of a man who, having once found a faith, is not going to lose it because of the injustices or cruelties inflicted by erring human instruments.” Communism or Catholicism: faiths not easily discarded for simple reasons of decency. It was, one might conjecture, faith itself that made Philby attractive to Greene over and beyond the allure of a considerable personal charm.
The two first met and became friends while employed as operatives in MI6. Recruited into the agency in 1941 by his own sister and posted to Sierra Leone, Greene remained involved in espionage for years thereafter, though the details are somewhat murky.
More here.