Rom 3:24, Gen 3:15, 2 Pt 2:5, Heb 11:7, Rom 1:17
Noah believed in the coming Christ because he had received favor from God. So Noah became righteous. (Genesis 3:15, Genesis 6:8-9, Romans 3:24, Romans 1:17)
Genesis 3:15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
Genesis 6:8 But Noah found grace in the eyes of the Lord. 9 These are the generations of Noah: Noah was a just man and perfect in his generations, and Noah walked with God.
Romans 3:24 Being justified freely by his grace through the redemption that is in Christ Jesus:
Romans 1:17 For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
Noah built the ark at the command of God, preaching the righteousness of God, Christ. (2 Peter 2:5, Hebrews 11:7)
2 Peter 2:5 And spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly;
Hebrews 11:7 By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house; by the which he condemned the world, and became heir of the righteousness which is by faith.