Thanks for your inquiry. Let us first address this question: Did everyone other than Noah's family die in the great flood?

The answer is yes: everyone outside of Noah's family perished in the flood. Recall from Genesis 6 that the context of and reason for the flood was rampant sin and wickedness on the part of human beings. In only a few generations since the rebellion of Adam and Eve, the stench of man's sin in the earth had become unbearable to God. Genesis 6:5 paints a dismal portrait of the world: man's thought processes were thoroughly corrupt, and his actions, consequently, were heinous. Because of sin the human race had failed miserably to fulfill its God-given mandate (to glorify and to live before God in all of life) -- thus the Lord, who is of purer eyes than to behold our sin, executed judgment on a guilty and unrepentant race (that deserved such punishment).

By God's grace, however, one man -- Noah -- had been obedient to the Lord. God therefore chose to deliver Noah even as He judged the rest of humanity. Noah was spared only because of God's grace, which already had worked in him a repentant and believing heart.

Some people have difficulty understanding and agreeing with the biblical doctrine of "limited atonement." Yet the reality is that all humans are sinners and therefore deserve the wrath of God, but of God's great mercy He has chosen to save some men. And, of course, those whom He has chosen will come to Him through God-given repentance and faith in Christ as their Redeemer. Not everyone will be saved. Not everyone will go to heaven. These, in fact, do not desire to go to heaven! In a weak, pluralistic age such as ours, when everyone save mass-murderers is made to believe he or she will go to heaven, the account of the flood reminds you and me that 1) salvation is totally the work of God's free grace and 2) not every human being will go to heaven. God Himself limits the Atonement of Calvary -- foreshadowed by Noah's Ark in the Old Testament -- to His elect.

In the second part of your query, you mentioned the sin of incest and, we might infer, questioned why the Lord would sanction such relations here (and in the earlier portions of Genesis) yet forbid it later in Scripture. To untie this apparent knot, you and I first must observe that the Scriptures are the authoritative Word of our God and King. He has the right as God to reveal what He chooses; and His Word is our final authority. We therefore trust the Word of God and submit to its teaching.

Yet you and I also must remember that God is Lord of creation and displays His glory (and works out His eternal plan) through creation. In biblical times, before the canon of Scripture was final and we had the perfect revelation of God in Christ and in Scripture, the Lord would work through miracles to reveal His power and to unfold His plan of redemption. For example, God parted the Red Sea to show Himself to be the one true God *and* to deliver His chosen people from their enemy. Fast forward several hundred years to the time when Christ rose from the dead, revealing His power over life and death *and* delivering his people from their last enemy -- death. God controls nature, and He does so to work out His own saving purposes.

It was logically necessary to have such close relations after the creation of Adam and Eve in order to propagate the human race. And when man's guilt required that our holy Lord destroy sinners from the earth, it again was logically necessary for such close relations -- this time among Noah's family -- to be the vehicle by which the earth was replenished. We do well to observe that by Noah's time, the family tree of humanity had broadened considerably from the earliest days of man. You and I also must recall that, as stated earlier, God is Lord of creation, and His superintendence over this reproduction to ensure a genetically stable race is logical *and* expected. In other words, it makes sense that God can do exactly what He wants with His creation in order to further His plans for His world: to deny this truth would make the Creator subject to the creation!

As we are told in Scripture (I Corinthians 13:8b), true miracles of nature -- such as speaking in tongues and the parting of seas -- no longer occur. The Lord has revealed His power and His salvation perfectly in our Lord Jesus Christ, thus we no longer need miracles to show us God's might and grace. By His goodness the earth has been repopulated; we must not turn to family relations to continue the human race but must utilize His ordinary means of propagation. According to God's Word and will, such familial relations are sinful because they are no longer necessary for survival but in fact promote lust, aberrance and decay of all sorts.

In sum, remember that God has spoken, and His Word is final. While it is a Word of judgment to those who refuse to bend the knee to Him and to embrace His Son, it is -- thankfully -- a Word of grace to those who will hear and believe.