Why then would God allow sin in the first place? He was not responsible for it, but it came from the reasonings that were made by His creatures, based upon the information God had given them. Was He caught off guard by it? No. God did decree to use evil as a part of His eternal plan, to use it for His purposes. So back to the question, why did God allow it?

1. In order for God to save sinners He had to allow sin. In order to show His mercy He had to allow sin. How could He show those parts of His nature if there were no sin in the world? How could He show His love to even His enemies, if there are no enemies to love?

2. He allows sin in order to display His wrath, anger and judgement which are also a part of His nature. All throughout history we see the salvation of sinners and the damnation of sinners and we see places prepared for both. The eternal purpose of God was to save some and judge some in order that He might show us both His grace and His wrath.

3. In time He will totally destroy it forever. As long as His creatures have any freedom at all - as long as they have intelligence and reason and choice - there will be evil/sin because they will have the potential to fall short of God’s standard. Everyone makes wrong choices. When all of the history of redemption is complete, death, hell and judgement will be cast into the lake of fire. There will be no more sadness or pain or disease no more sin.

We can say rather than the issue being fatalistic, that God, within His decree, allowed for choice knowing what those choices would be, and planned those things so that both His grace and wrath might be displayed, and that sin might eventually be disposed of permanently.

I agreed completely with your first part. However I would state the second part differently.

God didn't allow sin to save sinners. He could save sinners without sin.(God never wanted people to sin in the first place.)

1. The reason sin came into being was because God wanted people (and all of His creation) to love Him of "their own free will".

It is all about love.

God's purpose for free will was for man, made in his image, to love him and have a relationship with him.

Original sin came into being from within the heart of free will of both Satan first and man, later. All beings of God's creation have a free will to love God or disobey Him.

God saw that sin would happen but love can only happen when it is given freely of own free will.

God knew that he would reconcile his world at the fullness of time.

Once each man decides, of their own free will, whether they choose God or this world. God will one day end "free will" and the men that have chosen to be with Him/Christ, will share His will.

God's wrath comes from man's disobedience.

God's wrath comes from God's jealousy over the fact that He, God, is the creator and man disobediently puts many things before God.

God is very patient and it is His purpose to show His mercy. God is a merciful, Loving Heavenly Father.

God desires all men to be saved.

Titus 2:11 For the grace of God has appeared for the salvation of all men.

For God so loved the world...

“God didn't allow sin to save sinners. He could save sinners without sin”

****This doesn’t make sense - save them from what?

“The reason sin came into being was because God wanted people (and all of His creation) to love Him of "their own free will".”

***The reason sin came into the world was because Satan and then man chose to disobey God.

“God's wrath comes from man's disobedience.
God's wrath comes from God's jealousy over the fact that He, God, is the creator and man disobediently puts many things before God.”

***Wrath is a part of God’s character. If God never changes; has, is and always will be the same, then His wrath has, is and always will be part of Him. Therefore it was present before there even was an angel or man to sin. And as I already said “He allows sin in order to display His wrath, anger and judgement which are also a part of His nature.”
Consider
Romans 9:22 - “What if God, WANTING TO SHOW HIS WRATH and TO MAKE HIS POWER KNOWN, endured with much longsuffering the vessels of wrath prepared for destruction and that He might MAKE KNOW THE RICHES OF HIS GLORY on the vessels of mercy, which He had prepared beforehand for glory…”

Seems pretty clear to me.

Romans 9:22

Says, What if? It doesn't say, It is.

1 John 4:8 He who does not love does not know God; for God is love.

Seems pretty clear to me.

God has no need for wrath unless his creation disobeys.