18 Yoke yourself under the law, that you may be a freeman in very truth. Work not the desire of your soul apart from the law of God. How many commandments must I write, and how many laws must I engrave; which, if you desire your freedom, you can learn all from yourself? And if you love purity, you will teach it to others also. Let nature be your book, and all creation your tables; and learn from them the laws, and meditate things unwritten. The sun in his course teaches you that you rest from labour. The night in her silence cries to you that a limit is set to your works. The earth and the fruit of the tree cry that there is a season for all things. The seed you sow in the winter, in the summer you gather its harvest. Thus in the world sow seeds of righteousness, and in the Resurrection gather them in. The bird in its daily gleaning reproves the covetous and his greed, and rebukes the extortion that grasps the store of others. Death, the limit of all things, is itself the reprover of all things.
Source: On Admonition and Repentance (New Advent)