Noah distinguished himself from among his contemporaries for being “a just man, perfect in his generations”: at this point in time we have no information whether God had given men some kind of written law, but there was conscience of what was God´s will, and those who complied with it are said to “have walked with God”: Noah, like Enoch, walked with God.
Mankind had no excuse for departing from God:
By the very old age reached by the antediluvian people undoubtedly there would have been direct communication from Adam to Methuselah and from the latter to Noah. Adam knew God before being expelled from the Garden of Eden, and his descendants, particularly those in the line to Noah, described in the previous chapter, were made aware of what was right and pleasing to God.
God had promised a Redeemer, a descendant of Eve.
Adam and Eve had learned that there needed to be an offering of blood to cover their sin. Abel obeyed, but his brother Cain chose to make an offering of his own taste, which was rejected by God.
Enoch prophesied in his time, announcing the coming of the Lord in the future, with his saints, to install his kingdom on earth.
Noah was a preacher at the end of the period.
The Holy Spirit of God acted in people.
Like Adam, they had an alternative to either walk with God, loving Him and serving Him with sincerity, or to go their own way, becoming rebellious and selfish. All were endowed with a conscience which accused them when they did what was wrong
As we begin this report we see that all flesh had unfortunately corrupted their way on earth except for Noah who, righteous and sincere, was favoured by God. The rest of mankind, corrupt and filled with violence, was doomed to destruction.
God communicated directly with Noah (we do not know how - but probably in the same way that He communicated with others in antiquity, as Adam and Cain), and gave him specific instructions to build an ark. It was not a ship or boat, because its purpose was not to sail, but only to float, sheltering eight people and many animals from the storm outside, and their provisions.
Its format was therefore quadrangular, of gigantic dimensions even in our times: 133 metres long, 22 metres wide and 13 metres high (assuming a cubit measured 44 cm at that time, as in the time of Hezekiah some 1,700 years later) therefore with a volume of 38,038 cubic meters.
The ark was made of wood, with an opening all round 44 cm wide (for air renewal), a single door on one side and three floors inside with a total area of more than 8,700 square meters. The fact that there was only one door reminds us that the Lord Jesus taught that He is “the door” of salvation.
We understand from Genesis 2:6 and 9:14-16 that it had not yet rained upon the earth. Noah was certainly a faithful man, obedient and full of faith in God to carry out such an enterprise! Everything indicates that he took 120 years to build the ark!
In Hebrews 11:7 we read that “by faith Noah being divinely warned of things not yet seen, moved with godly fear, prepared an ark for the saving of his household, by which he condemned the world and became heir of the righteousness which is according to faith.” Noah is mentioned by God in Ezekiel 14:13-20 as one of three men - Job and Daniel are the other two – which because of their righteousness would be delivered from four severe judgments of God, the sword, famine, wild beasts and pestilence, but no one else, even their own children. We read in 2 Peter 2:5 that Noah was a preacher of righteousness.
Noah's situation resembles that of true believers in Christ today:
We are righteous, justified by the blood of Christ.
Humanity in general at the time of Noah was disobedient, though long-suffering God waited while the ark was being prepared, and only eight people were saved; so mankind today continues to be disobedient, and very few repent and turn to God: “the gate is narrow, and difficult is the way which leads to life, and there are few who find it”, as our Saviour foretold (Matthew 7:13-14).
The ark was a type of baptism: not the exterior ceremony, but what it represents, death with Christ and a resurrection with a clear conscience before God (1 Peter 3:20-21).
God announced that the flood would be total: every man and all animals which moved and crept over the earth and breathed on dry land would die because the water would cover the entire surface of the earth and all the high hills under heaven. But Noah, his children, his wife and his daughters in law would enter the ark and Noah should put in it “even each of every clean animal, a male and his female; two each of animals that are unclean, a male and his female; also seven each of birds of the air, male and female”, to keep the species alive for afterwards. They would all come to him, and he must also take all food for himself and the animals (we assume that they were still all vegetarian, as they were created).
Noah obediently did everything as God commanded him.
9 This is the genealogy of Noah. Noah was a just man, perfect in his generations. Noah walked with God.
10 And Noah begot three sons: Shem, Ham, and Japheth.
11 The earth also was corrupt before God, and the earth was filled with violence.
12 So God looked upon the earth, and indeed it was corrupt; for all flesh had corrupted their way on the earth.
13 And God said to Noah, "The end of all flesh has come before Me, for the earth is filled with violence through them; and behold, I will destroy them with the earth.
14 Make yourself an ark of gopherwood; make rooms in the ark, and cover it inside and outside with pitch.
15 And this is how you shall make it: The length of the ark shall be three hundred cubits, its width fifty cubits, and its height thirty cubits.
16 You shall make a window for the ark, and you shall finish it to a cubit from above; and set the door of the ark in its side. You shall make it with lower, second, and third decks.
17 And behold, I Myself am bringing floodwaters on the earth, to destroy from under heaven all flesh in which is the breath of life; everything that is on the earth shall die.
18 But I will establish My covenant with you; and you shall go into the ark—you, your sons, your wife, and your sons' wives with you.
19 And of every living thing of all flesh you shall bring two of every sort into the ark, to keep them alive with you; they shall be male and female.
20 Of the birds after their kind, of animals after their kind, and of every creeping thing of the earth after its kind, two of every kind will come to you to keep them alive.
21 And you shall take for yourself of all food that is eaten, and you shall gather it to yourself; and it shall be food for you and for them."
22 Thus Noah did; according to all that God commanded him, so he did.
Genesis chapter 6, verses 9 to 22