clean. Noah would have known of the distinction between clean and unclean through special revelation (5:22 note). Fundamental institutions of the Law—the Sabbath (2:1–3), the ideal sanctuary (2:8 note), and sacrifice (3:21; 4:3–5)—reach back to the pre-Flood creation order; others, such as tithing (14:20) and circumcision (17:9–14), to at least the time of the patriarchs. Earth’s future depended on these sacrificial animals (8:20–22 and notes; Lev. 11:1–47 note).