De Plantatione

And Moses very appropriately says that the fruit of education is not only holy but also praised; for every one of the virtues is a holy thing, but most especially is gratitude holy; but it is impossible to show gratitude to God in a genuine manner, by those means which people in general think the only ones, namely offerings and sacrifices; for the whole world could not be a temple worthy to be raised to his honour, except by means of praises and hymns, and those too must be such as are sung, not by loud voices, but by the invisible and pure mind, which shall raise the shout and song to him.