The Classic of the Green Bag is an early foundational text on feng shui, explaining its principles through a system of numerical symbolism and the interplay of yin and yang. The text establishes a cosmology where heaven and earth, represented by numerical pairings, interact to create the five elements and eight trigrams. These elements and trigrams, further organized by directional alignments, demonstrate the continuous flow of qi, crucial for understanding environmental harmony and balance within feng shui practice. The text's core concept emphasizes the transformative power of yin and yang's interconnectedness.