Describing the creation of the heavens and earth in Genesis the word one day is translated from the Hebrew word YOM and YOM and has many meanings depending on it’s context. One meaning that makes more sense to me is age. Considering carbon dating, the fossil record and more, the 7 days (7 ages) of creation could be a mixture of  days or thousands or millions or  billions of years of time or one day 

Genesis 1 The First Age: In the beginning God created the heavens and the earth. And the earth was formless and void, and darkness was over the surface of the deep; and the Spirit of God was moving over the surface of the waters. Then God said, “Let there be light”; and there was light. And God saw that the light was good; and God separated the light from the darkness. And God called the light day, and the darkness He called night. And there was evening and there was morning, one age.

Genesis 1 v6,The Second Age: Firmament. . . the vast solid dome of water created to divide the sea into upper and lower portions so that the dry land could appear.
Then God said, “Let there be an expanse in the midst of the waters, and let it separate the waters from the waters.” And God made the expanse, and separated the waters which were below the expanse from the waters which were above the expanse; and it was so. And God called the expanse heaven. And there was evening and there was morning, a second age.

Genesis 1 v9, The Third Age: Dry Ground . . Then God said, “Let the waters below the heavens be gathered into one place, and let the dry land appear” Let the earth sprout vegetation, plants yielding seed, and fruit trees bearing fruit after their kind, with seed in them, on the earth”; and it was so. And the earth brought forth vegetation, plants yielding seed after their kind, and trees bearing fruit, with seed in them, after their kind; and God saw that it was good. And there was evening and there was morning, a third age.              NOTE: (All vegetation and fruit and seeds produce after their kind because creation includes DNA!)

Genesis 1 v14, The Fourth Age: Sun, Moon, Stars . . Then God said, “Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs, and for seasons, and for days and years; and let them be for lights in the expanse of the heavens to give light on the earth”; and it was so. And God made the two great lights, the greater light to govern the day, and the lesser light to govern the night; He made the stars also. And God placed them in the expanse of the heavens to give light on the earth, and to govern the day and the night, and to separate the light from the darkness; and God saw that it was good. And there was evening and there was morning, a fourth age.

Genesis 1 v20, The Fifth Age: Fish and Birds . . Then God said, “Let the waters teem with swarms of living creatures, and let birds fly above the earth in the open expanse of the heavens.” And God created the great sea monsters, and every living creature that moves, with which the waters swarmed after their kind, and every winged bird after its kind; and God saw that it was good. And God blessed them, saying, “Be fruitful and multiply, and fill the waters in the seas, and let birds multiply on the earth.” And there was evening and there was morning, a fifth age.     NOTE: (after their kind because creation includes DNA!)

Genesis 1 v24, The Sixth Age: Creatures on Land . . Then God said, “Let the earth bring forth living creatures after their kind: cattle and creeping things and beasts of the earth after their kind:”; and it was so. And God made the beasts of the earth after their kind:, and the cattle after their kind:, and everything that creeps on the ground after its kind; and God saw that it was good. Then God said, “Let Us make man in Our image, according to Our likeness; and let them rule over the fish of the sea and over the birds of the sky and over the cattle and over all the earth, and over every creeping thing that creeps on the earth.” And God created man in His own image, in the image of God He created him; male and female He created them. And God blessed them; and God said to them, “Be fruitful and multiply, and fill the earth, and subdue it; and rule over the fish of the sea and over the birds of the sky, and over every living thing that moves on the earth.” Then God said, “Behold, I have given you every plant yielding seed that is on the surface of all the earth, and every tree which has fruit yielding seed; it shall be food for you; and to every beast of the earth and to every bird of the sky and to every thing that moves on the earth which has life, I have given every green plant for food”; and it was so. And God saw all that He had made, and behold, it was very good. And there was evening and there was morning, the sixth age.  NOTE: (Every creation includes DNA!)

Genesis 2 , The seventh age or day: The Creation of Man and Woman . .
Genesis 2 v7-9 Then the LORD God formed man of dust from the ground, and breathed into his nostrils the breath of life; and man became a living being. And the LORD God planted a garden toward the east in Eden and there He placed the man whom He had formed. And out of the ground the LORD God caused to grow every tree that is pleasing to the sight and good for food; the tree of life also in the midst of the garden, and the tree of the knowledge of good and evil.
Genesis 2 v16-17 And the LORD God commanded the man, saying, “From any tree of the garden you may eat freely; but from the tree of the knowledge of good and evil you shall not eat, for in the day that you eat from it you shall surely die.”
Genesis 2 v18 Then the LORD God said, “It is not good for the man to be alone; I will make him a helper suitable for him.”
Genesis 2 v21-22  So the LORD God caused a deep sleep to fall upon the man, and he slept; then He took one of his ribs, and closed up the flesh at that place. And the LORD God fashioned into a woman the rib which He had taken from the man, and brought her to the man. 

Genesis 3  The Fall of Man:
Genesis 3 v1-7  Now the serpent was more crafty than any beast of the field which the LORD God had made. And he said to the woman, “Indeed, has God said, ‘You shall not eat from any tree of the garden’?” And the woman said to the serpent, “From the fruit of the trees of the garden we may eat; but from the fruit of the tree which is in the middle of the garden, God has said, ‘You shall not eat from it or touch it, lest you die.’” And the serpent said to the woman, “You surely shall not die! “For God knows that in the day you eat from it your eyes will be opened, and you will be like God, knowing good and evil.” When the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was desirable to make one wise, she took from its fruit and ate; and she gave also to her husband with her, and he ate. Then the eyes of both of them were opened, and they knew that they were naked; and they sewed fig leaves together and made themselves loin coverings.

When the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was desirable to make one wise, she took from its fruit and ate; and she gave also to her husband with her, and he ate. Then the eyes of both of them were opened, and they knew that they were naked; and they sewed fig leaves together and made themselves loin coverings.

Now to answer the question why does every human require the gift
of forgiveness and salvation from God ?

When Eve stole the fruit from the tree of the knowledge of good and evil and ate it and gave it to Adam and he ate it, their DNA changed!
DNA changed for all of Humanity!
Human DNA was without a sinful nature before they ignored the only commandment God gave them.
Now the human DNA code has a sin chromosome that is passed on to every human.
This separated the human race from God  (Romans 3:23  for all have sinned and fall short of the glory of God)
Since the penalty of sin is death and total separation from God for the human race, God chose to accept the judgement Himself in the person of Jesus the Messiah.