The modern liturgical movement has taken many years to find its dogmatic and really deep spiritual basis. It has received its confirmation in this regard from the two great Papal Encyclicals, Mystici Corporis and Mediator Dei; while the whole movement has depended upon, as well as influenced, the abandonment of the post-reformation, literal explanation of the Sacrifice of the Mass and on the return to the priestly and sacramental understanding of it. This conversion of the theologians, the effects of which are now reaching the ordinary Catholic, is due in the first place to Père de la Taille, S.J., whose heavily documented Mysterium Fidei exploded like some doctrinal atom bomb just after the 1914-18 war. It is a happy coincidence that the second volume of the English translation of this revolutionising work should have just appeared,! for it deals with the Church’s sacrifice as offered by the priest at Mass and united with the unique act of Calvary. Although Père de la Taille did not fully escape from the unreal terminology of the post-reformation disputes he sets forth in this volume the principles which in fact underlie the point of view of the outstanding modem writers on the Eucharist such as Abbot Vonier or Dom Casel. His clear distinction between immolation and oblation has been regarded as his special contribution to the development of Eucharistic doctrine; yet the approach here is still the over-literal one which considers only the present sacrifice here on the altar and fails to appreciate the full significance of a sacramental sacrifice. It was easy to dispose of those almost crude theories of the ‘mystic sword’ which would slay Christ once again did he not remain impassible, but it was not such a straightforward task to escape being involved in the mechanics of the Mass as though it had to fulfil some man-made definition of a sacrifice.