一切真言心

The first Sanskrit letter '(sa) a'; it is pronounced 'an' by the Shingon School and emphasized as the heart of all wisdom. In India '(sa) a' is the 'name of Vishṇu (especially as the first of the three sounds in the sacred syllable (sa) oṃ or (sa) aum), also of Brahmā, Śiva, and Vaiśvānara (Agni)' M. W.