The LORD saw that the wickedness of man was great in the earth, and that every intention of the thoughts of his heart was only evil continually.

And the LORD regretted that he had made man on the earth, and it grieved him to his heart. So the LORD said, "I will blot out man whom I have created from the face of the land, man and animals and creeping things and birds of the heavens, for I am sorry that I have made them."

But Noah found grace in the eyes of the LORD.

The Lord God (Jehovah) looked at the earth and saw that the wickedness of mankind was great, and every imagination of the thoughts of their heart was evil continually. But we read of a very small remnant – Noah who found grace or favour in Jehovah, and in that mercy is shown. It was not Noah's goodness, but rather because of his faith in Jehovah a means of escape was provided (Hebrews 11:7). More importantly Jehovah had promised a son that would be a means of salvation (Genesis 3:15); Noah was the conduit to Jesus. Note also that Noah "found" grace - it was not won nor worked for, but rather Noah turned to Jehovah and found grace in God.
God's patience is evident, because it took Noah some 120 years to build an ark which he built "in reverent fear". This is the believer's position today – working out your own salvation in fear and trembling (Philippians 2:12).  Not also the rainbow is not evidence of no further judgement, but rather the means of judgement would not be by flood (Genesis 9:13-17) - judgement will be executed by Christ at the fulness of times (Romans 2:3; 2 Timothy 4:1). Sin fills this earth - men do not speak of it, within or without the church. Thus the situation of sinfulness, similar to that of Noah's time, is apparent today; there is a small remnant through faith who are saved from the coming judgement by Christ (Ephesians 2:8). For we read Jehovah’s verdict, "for [man] he indeed is flesh."  And God said to Noah, "I have determined to make an end of all flesh, for the earth is filled with violence through them. Behold, I will destroy them with the earth." (Genesis 6:13)