Noah was a righteous man in the sight of God (Gen. 6:9). Thus he became the central figure of the providence and for 120 years built the ark as a conditional object, laying the foundation of faith acceptable to God.
Because of the vertical relationship with God which Noah established through his absolute faith, a history of judgment could begin. God exercised the flood judgment to destroy the rest of mankind because they would not change their evil ways and stand on God's side along with Noah (Gen. 6:13).