But a foundation is not to be mistaken for superstructure: a full-fledged and developed religion needs a great deal more than foundation—there must be a building too. The warmth and vitality imparted by strong religious conviction is a matter of common observation, and is a force of great magnitude; but it is a personal and living thing, it cannot be embodied in a formula or taught in a class. Here lies the proper field of work of the Churches. What can be taught in a school is the fundamental substratum underlying all such developments and personal aspirations; and it can be dealt with on a basis of historical and scientific fact, interpreted and enlarged by the perceptions and experiences of mankind. A creed or catechism should not be regarded as something superhuman, infallible, and immutable; it should be considered to be what it really is—a careful statement of what, in the best light of the time, can be regarded as true and important about matters partially beyond the range of scientific knowledge: it must always reach farther into the unknown than science has yet explored. An element of mystery and difficulty is not inappropriate in a creed, although it may be primarily intended for comprehension by children. Bare bald simplicity of statement, concerning things keenly felt but imperfectly known, cannot be perfectly accurate; and yet every effort should be made to combine accuracy and simplicity to the utmost. Every word should be carefully weighed and accurately used: mere conventional terminology should be eschewed. A sentence stored in the memory may evolve different significations at different periods of life, and at no one period need it be completely intelligible or commonplace. The ideal creed should be profound rather than explicit, and yet should convey some sort of meaning even to the simplest and most ignorant. Its terms, therefore, should not be technical, though for full comprehension they would have to be understood in a technical or even a recondite sense.