The flood demonstrates that those who depart from God become increasingly evil and violent towards their fellow man.
Genesis 6:5 And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
Genesis 6:11 The earth also was corrupt before God, and the earth was filled with violence. 12 And God looked upon the earth, and, behold, it was corrupt; for all flesh had corrupted his way upon the earth.
The evil that comes from within men was not destroyed at the flood. It is still resident in the descendents of Noah (all of us).
Mark 7:21 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, 22 Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: 23 All these evil things come from within, and defile the man.
The flood shows that God will destroy the wicked and preserve the righteous.
Psalms 145:20 The LORD preserveth all them that love him: but all the wicked will he destroy.
Noah believed God and was saved by his faith.
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.
His experience demonstrates that ‘the just shall live by faith’.
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 found grace (favour) in his God’s sight because he was ‘just’ man who walked with God.
Genesis 6:8 But Noah found grace in the eyes of the LORD.9... Noah was a just man and perfect in his generations, and Noah walked with God.
Hebrews 11:6 ...he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.
Noah was a preacher of righteousness; preaching is an act of faith.
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;
Peter uses the flood to support the prophetic warning that there is to be another day of judgment in the future.
2 Peter 3:6 Whereby the world that then was, being overflowed with water, perished: 7 But the heavens and the earth, which are now, by the same word are kept in store, reserved unto fire against the day of judgment and perdition of ungodly men... 9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance. 10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.
11 Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness, 12 Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat? 13 Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness.
The flood was literal and destroyed every living thing outside of the Ark but we are not to suppose that the physical heavens and earth are going to be destroyed by fire. Peter is speaking metaphorically. The heavens and earth to be destroyed are the present political order of government. There are ample scripture references which show that the earth is to be restored as the kingdom of God, with its capital at Jerusalem.
Luke 1:32 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David: 33 And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
In the millennial reign of Christ there will be a mortal population which survive the judgments.
Micah 4:1 But in the last days it shall come to pass, that the mountain of the house of the LORD shall be established in the top of the mountains, and it shall be exalted above the hills; and people shall flow unto it. 2 And many nations shall come, and say, Come, and let us go up to the mountain of the LORD, and to the house of the God of Jacob; and he will teach us of his ways, and we will walk in his paths: for the law shall go forth of Zion, and the word of the LORD from Jerusalem. 3 And he shall judge among many people, and rebuke strong nations afar off; and they shall beat their swords into plowshares, and their spears into pruninghooks: nation shall not lift up a sword against nation, neither shall they learn war any more. 4 But they shall sit every man under his vine and under his fig tree; and none shall make them afraid: for the mouth of the LORD of hosts hath spoken it.
Those who ignored the preaching of Noah and the visible construction of the Ark perished. In our day those who ignore the preaching of the gospel of Christ will also perish.
The gospel of God’s promised saviour was known in the days prior to the flood. It was on the basis of one who would take away sin that men of old like Noah walked with God.
The survival in the Ark passing through the waters of flood is said to be a type or figure of baptism by which those who believe and obey the gospel can be saved today.
1 Peter 3:20 Which sometime were disobedient, when once the longsuffering of God waited in the days of Noah, while the ark was a preparing, wherein few, that is, eight souls were saved by water. 21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
Jesus uses the peoples’ refusal to believe that a flood was coming to demonstrate that people will be likewise unprepared for his second coming.
Luke 17:26 And as it was in the days of Noe, so shall it be also in the days of the Son of man. 27 They did eat, they drank, they married wives, they were given in marriage, until the day that Noe entered into the ark, and the flood came, and destroyed them all.
In the same way that God appointed a day for the flood so he has appointed a day for the judgment of this present world.
Acts 17:31 Because he hath appointed a day, in the which he will judge the world in righteousness by that man whom he hath ordained; whereof he hath given assurance unto all men, in that he hath raised him from the dead.
The message to repent of our evil way of life and accept God’s way of escape from death is as vital today as it was in Noah’s day.
I hope you have found this helpful.