It is understood that man described God in a way he/she related to at the time. It is understood that humanity in the OT was immature, childish or adolescent in behavior. At one point they all followed God's commands, then fail, then back again after suffering, then fail, then back again, then fail, and so on and so forth. The story of Israel is one with equally both praise and rebuke. God was like a Father who pretty much praises their good deeds and terrifies them with their bad deeds, not that God is wrathful in any literal sense. His wrath was that like a parent to a little child so that they can be geared towards the right way. Also keep in mind, many of the stories really is not God punishing them directly, but rather letting them see for themselves the consequences of their own actions...
So basically since man kept falling down and back up,
Some got back up. Others just fell further down.
Christ had to come to show us the way. That is why God became man?
Only in part: God the Son became man so that His relationship with God the Father could become our relationship with the Father. Not taking us in like foster children, to be given an example of a good family and then sent back, but rather adoption into the divine family of the Holy Trinity. In baptism our realtionship with God is not like that between Jesus and the Father, it is that relationship between Jesus and the Father. As the baptismal hymn says "As many as are baptized into Christ, have put on Christ." As St. Peter writes in his second epistle:
1:1 Simeon Peter, a servant and apostle of Jesus Christ, To those who have obtained a faith of equal standing with ours in the righteousness of our God and Savior Jesus Christ: 2 May grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord. 3 His divine power has granted to us all things that pertain to life and godliness, through the knowledge of him who called us to his own glory and excellence, 4 by which he has granted to us his precious and very great promises, that through these you may escape from the corruption that is in the world because of passion, and become partakers of the divine nature
. 5 For this very reason make every effort to supplement your faith with virtue, and virtue with knowledge, 6 and knowledge with self-control, and self-control with steadfastness, and steadfastness with godliness, 7 and godliness with brotherly affection, and brotherly affection with love. 8 For if these things are yours and abound, they keep you from being ineffective or unfruitful in the knowledge of our Lord Jesus Christ.
As Pope St. Athanasius the Great of Alexandria, the Great Champiion of the Faith of Nicea, states: "God became man so that man could become God." Not according to the lie of the serpent, which led to death, but according to His Word "'Let Us create Man in Our Image and Likeness'....And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul."
And what about setting the stage for the Incarnation? I mean isn't the OT about setting up the savior as well?
The OT has no other purpose.
I have a question, did Christ fulfill every single prophecy in the OT? And how many prophecies were there?
There are hundreds referenced in the NT itself, and thousands which the Fathers (and Mothers!) of the Church reference. To give an exmple of one not in the NT, but expounded from the earliest days of the Church, Isaiah 66:
1 Thus says the LORD:
"Heaven is my throne and the earth is my footstool;
what is the house which you would build for me,
and what is the place of my rest?
2 All these things my hand has made,
and so all these things are mine,
says the LORD.
But this is the man to whom I will look,
He that is humble and contrite in spirit, and trembles at my word.
3 "He who slaughters an ox is like him who kills a man;
he who sacrifices a lamb,
like him who breaks a dog's neck;
he who presents a cereal offering,
like him who offers swine's blood;
he who makes a memorial offering of frankincense,
like him who blesses an idol.
These have chosen their own ways,
and their soul delights in their abominations;
4 I also will choose affliction for them,
and bring their fears upon them;
because, when I called, no one answered,
when I spoke they did not listen;
but they did what was evil in my eyes,
and chose that in which I did not delight."
5 Hear the word of the LORD,
you who tremble at his word:
"Your brethren who hate you and cast you out for my name's sake have said,
'Let the LORD be glorified, that we may see your joy';
but it is they who shall be put to shame.
6 "Hark, an uproar from the city!
A voice from the temple!
The voice of the LORD,
rendering recompense to his enemies!
7 "Before she was in labor she gave birth;
before her pain came upon her she was delivered of a son
8 Who has heard such a thing?
Who has seen such things?
Shall a land be born in one day?
Shall a nation be brought forth in one moment?
For as soon as Zion was in labor she brought forth her sons.
9 Shall I bring to the birth and not cause to bring forth?
says the LORD;
shall I, who cause to bring forth, shut the womb?
says your God.
10 "Rejoice with Jerusalem,
and be glad for her,
all you who love her; r
rejoice with her in joy,
all you who mourn over her;
This Prophecy was fulfilled at the Nativity of Our Lord, and God, and Savror, i.e. Christmas, because the Church teaches that the Virgin Mary, the New Eve, gave birth to Christ, the New Adam without labor pains. The reason is that from the first moment, Christ was undoing the curse at the expulsion from Paradise, Genesis 3:
14 The LORD God said to the serpent,
"Because you have done this,
cursed are you above all cattle,
and above all wild animals;
upon your belly you shall go,
and dust you shall eat all the days of your life.
15 I will put enmity between you and the woman,
and between your seed and her seed;
He shall crush your head,
and you shall bruise his heel."
16 To the woman he said,
"I will greatly multiply your pain in childbearing;
in pain you shall bring forth children
yet your desire shall be for your husband,
and he shall rule over you."
Because the Holy Theotokos ("She who gave birth to God") listened to God and not the serpent, she gave birth to the New Adam without the pains of Eve. Instead, however, she experienced the pain of seeing her son and God dying on the Cross, where He crushed the head of the serpent. Btw, according to Tradition, Golgotha, "the place of the Skull" got its name from Father Adam's skull being buried there. You'lll see it on most icons of the Crucifixion.
But back to your question. It may be better to say that He is fulfilling all the prophecies, as there were those on His first coming (which have all been fulfilled), some which were fulfilled during the time of the Apostles, some the Church has fulfilled since then, and some which will be fulfilled at the second coming. (btw, it is often said that the Jews are conflating the prophecies of the first and second coming, which is why they are still waiting for someone who has already come).