It hardly needs saying that it is not easy to about the Trinity, at Least if one aims at being intelligible as well as verbally accurate. Yet this mysterious doctrine is certainly not of merely intellectual or speculative interest, with nobearing on practice. Quite the contrary. The fascination it has for the greatest Christian minds—St Augustine's for example or St Thomas's—has not been primarily the fascination of a more problem. These saints, in their endeavour to see as clearly as possible into the mystery of the three Persons, and even while they were perfectly aware that the reasoning that this effort entailed was too subtle to be followed by the majority of believers, never thought of themselves as engaged in a merely theoretical enquiry. They reasoned about the mystery as masters of Christian doctrine, but the mystery itself they knew as intimately involved in their own moral and religious lives, in their daily communion with Christ.