Not because God of OT is different from God of NT but because
Bible contains all sorts of characters—good and bad. So are its writers—good and bad.
God-dishonoring writers added such accounts which depict God as killer of humans and animals, and were so thoughtless that they added such accounts in Genesis Chapter 6, immediately after Genesis 5 where we read “God made mankind in HIS IMAGE.” (Genesis 5:1) In contrast, God-honoring writers wrote such things as Isaiah 66:3-4; Mathew 5:43-48; 10:29-31 etc.
God-dishonoring writers will have their agenda, and are thoughtless too. For example, immediately after saying things such as “With the measure you use, it will be measured to you” (Luke 6:38) we find Jesus is shown as supposedly declaring things such as Luke 7:26-28 contradicting himself and all known logic:
John the Baptist is not merely a prophet, but “more than a prophet.” (Luke 7:26)
“Among those born of women there is no one greater than John; yet the one who is least in the kingdom of God is greater than he.” (Luke 7:28)
In effect, it is like a king saying about a person: “This man is more than a father to me, but in my new palace which I am constructing now, he will be treated less than a house-servant.” What ingratitude it is, what logic it is!!!
And thoughtless interpreters would interpret it as saying “This is the proof that Jesus spoke of two different hopes—HEAVENLY and EARTHLY—and John the Baptist has only earthly hope, not heavenly hope.”
Thus agenda is implemented--two HOPES were introduced—Jesus as the first fruit to the heavenly hope and his chosen 144000 as belonging to “Kingdom of Heaven,” and all others as belonging to earthly hope called “Kingdom of God.”
This teaching belongs to God-dishonoring writers because Jesus taught both “Kingdom of God” and “Kingdom of Heaven” as one and the same, both are used interchangeably. (Mathew 19:23-24; 11:11; Luke 7:28) It is “Kingdom of Heaven” because the one who “restores and renews” is God the Father in the Heavens. (Mathew 6:9; 19:28; Acts 3:21) Its effects are enjoyed by people of “restored and renewed earth” hence its “Kingdom of God.” (Revelation 21:1, 5)
This only shows serpent is not one-time occurrence as shown in Genesis 3, but it is continuous. (1 Thessalonians 5:21)