When God created man He was sinless, and would have remained so had he not disobeyed the one restriction God gave him. God also told him what he would face as a penalty should he disobey that command.
Genesis 2:9, 16 & 17 KJV
9 And out of the ground made the LORD God to grow every tree that is pleasant to the sight, and good for food; the tree of life also in the midst of the garden, and the tree of knowledge of good and evil.
16 And the LORD God commanded the man, saying, Of every tree of the garden thou mayest freely eat:
17 But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
Had man not eaten from the tree of the knowledge of good and evil he would never have needed Redemption, because the Law of God would never have been evoked.
Romans 5:13 KJV
For until the law sin was in the world: but sin is not imputed when there is no law.
That one sin alone is sufficient to bring the Law into force, however that was only the beginning of man's disobedience of God as we see in the statement of Jesus.
Luke 11:49, 50 & 51
49 Therefore also said the wisdom of God, I will send them prophets and apostles, and some of them they shall slay and persecute:
50 That the blood of all the prophets, which was shed from the foundation of the world, may be required of this generation;
51 From the blood of Abel unto the blood of Zacharias, which perished between the altar and the temple: verily I say unto you, It shall be required of this generation.
As a further infuriation to God man not only continued to commit greater sins, but also rejected God himself.
Luke 12:47, 48, 49 & 50
47 And that servant, which knew his lord's will, and prepared not himself, neither did according to his will, shall be beaten with many stripes.
48 But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes. For unto whomsoever much is given, of him shall be much required: and to whom men have committed much, of him they will ask the more.
49 For I have not spoken of myself; but the Father which sent me, he gave me a commandment, what I should say, and what I should speak.
50 And I know that his commandment is life everlasting: whatsoever I speak therefore, even as the Father said unto me, so I speak.
A Loving and compassionate God in whom is no evil, would have been perplexed (if that is a proper term) as to why man would reject an opportunity to regain that friendship and closeness that God and man had in the Garden before man first sinned.
Ezekiel 18:23 & 24 , 13 & 14
23 Have I any pleasure at all that the wicked should die? saith the Lord GOD: and not that he should return from his ways, and live?
24 But when the righteous turneth away from his righteousness, and committeth iniquity, and doeth according to all the abominations that the wicked man doeth, shall he live? All his righteousness that he hath done shall not be mentioned: in his trespass that he hath trespassed, and in his sin that he hath sinned, in them shall he die.
13 When I shall say to the righteous, that he shall surely live; if he trust to his own righteousness, and commit iniquity, all his righteousnesses shall not be remembered; but for his iniquity that he hath committed, he shall die for it.
14 Again, when I say unto the wicked, Thou shalt surely die; if he turn from his sin, and do that which is lawful and right;
God being a just God, and would then have formulated a method by which man should be judged fairly. Since God cannot be tempted by Satan as man is it seems only logical that he provide a means by which man could be judged by a peer (that is to say one who also could be tempted by Satan).
Romans 5:12, 15 & 23
12 Wherefore, as by one man sin entered into the world, and death by sin; and so
death passed upon all men, for that all have sinned:
15 But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many.
23 For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord.
Therefore it would be necessary that someone whom Satan had tempted would be needed to sit in judgment of mankind. That Judge of mankind would not only have to be a peer, but would of necessity be without Sin himself otherwise he would be in the position of having to judge himself.
The way God chose to accomplish that is in the form of Jesus (the Christ).
John 5:22, 27 & 30
22 For the Father judgeth no man, but hath committed all judgment unto the Son:
27 And hath given him authority to execute judgment also, because he is the Son of
30 I can of mine own self do nothing: as I hear, I judge: and my judgment is just;
because I seek not mine own will, but the will of the Father which hath sent me.
God as one part of the tripartite God (in the form of the son or if you will Jesus) then assumed a human body in the infant born to the Virgin Mary.
At this point it must be understood why it must be a virgin birth.
When Adam and Eve sinned in the garden of Eden; Eve was deceived by Satan, but Adam was not. Adam had willfully sinned against God, while Eve sinned out of ignorance.
It is that willful sinning against God that is in need of forgiveness in that that is an exercise of free will, while Eve's sin was through being gullible and not the willful sin as was Adam who was not deceived.
When Jesus died on the cross he did so of his free will as a human, took on the burden of willful sin against the Tripartite God. In his accepting our burden of sin he negated all willful disobedience of God for anyone willing to allow him to do so.
For this reason it is necessary that mankind willingly accept Jesus death on the cross as his redemption from Sin.
The sentence of death God proscribed for man when said in that day you shall surely die was in reference not to physical death but to the second death described in Revelation.
But the fearful, and unbelieving, and the abominable, and murderers, and
whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the
lake which burneth with fire and brimstone: which is the second death.
That is why Jesus warned us in:
Matthew 10:28 KJV
And fear not them which kill the body, but are not able to kill the soul: but rather fear
him which is able to destroy both soul and body in hell.