This question, like the one I answered last time, was asked in a comment on my post about “Why did God create Satan?”
Q. If God is the same, yesterday, today and forever, why is He not dealing with our immoral, worldly society as He so often did in the Bible? Be it the flood, Sodom & Gomorrah, or any other references, He did not drag His feet, so to speak, and rendered swift judgment. The more I read the Bible, it seems like there are actually three different Gods in one, in the regard of how He was, is and will be.
At least as I understand it, the statement in Hebrews that “Jesus Christ is the same yesterday and today and forever” was intended to encourage second-generation followers of Jesus to hold fast to the faith they had been taught by His first-generation followers. (Right before this statement the author says, “Remember your leaders, who spoke the word of God to you. Consider the outcome of their way of life and imitate their faith.”) So this not so much an assertion that God, over the course of the whole Bible, has never changed the way He deals with humanity as it is a claim that we can continue to have confidence in the gospel, the good news about Jesus and what he has done for us, even though those who personally witnessed his earthly ministry have long passed away.
As for whether God deals with humanity differently now than He did in the Bible, here’s what I said about that in response to the question, “Does God change over the course of the Bible?”:
“From the start we see that God is consistent in his character qualities: creative, loving, generous, merciful even in judgment, and so forth. But these qualities do seem to get expressed in different ways as the divine-human relationship unfolds over the course of the Bible. . . . For example, when humans turn out to be so wicked, God regrets making them and destroys almost all of them through the flood. But afterwards, recognizing that ‘every inclination of the human heart is evil from childhood,’ he resolves never to destroy them all again.”
In other words, to use one of the examples you cited—the flood—God says explicitly in the Bible that He will not again respond to human wickedness the way He did at that time. I suggest in the same post I just quoted that “God himself actually changes in terms of how much relational experience He has with humans.” So it is not so much a case of there being three different Gods—a past judgmental one, a present merciful one, and a future judgmental one—but a matter of God’s relationship with us changing as it unfolds over history and experience.
The prelude to the gospel of John says that “the law was given through Moses; grace and truth came through Jesus Christ.” So we today are very blessed to live in a period of redemptive history when the mercy that is always balanced with justice in the character of God is at the forefront. But we must be careful not to presume on that mercy, but remember, in light of all the judgment passages you mentioned, as Peter writes in a long and unforgettable sentence (with which I will close):
“If God did not spare angels when they sinned, but sent them to hell, putting them in chains of darkness to be held for judgment; if he did not spare the ancient world when he brought the flood on its ungodly people, but protected Noah, a preacher of righteousness, and seven others; if he condemned the cities of Sodom and Gomorrah by burning them to ashes, and made them an example of what is going to happen to the ungodly; and if he rescued Lot, a righteous man, who was distressed by the depraved conduct of the lawless (for that righteous man, living among them day after day, was tormented in his righteous soul by the lawless deeds he saw and heard)— if this is so, then the Lord knows how to rescue the godly from trials and to hold the unrighteous for punishment on the day of judgment.”
Good Question 
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