God decided to show forth his goodness. And so he created man and woman so that he could share his everlasting happiness with them; to give them infinite bliss.
Amongst the other gifts he bestowed on them, he gave them free will. He wanted them to love him on their own accord... for true love is never forced. This love was to be proved by their obedience... but they rejected God by disobeying him; they made an insult onto the infinite God. Thus eternal happiness was forever denied to them, they would forever be separated from Love, which is God himself.
God in his infinite love and mercy could not bear that it be so. But the only way man and woman could be saved from their fate was if adequate reparation was made to his justice.
The problem was that since God is infinite, that made the insult given by humanity infinite, and hence the reparation that needed to be made had to be infinite in order to be adequate. Justice also required that the debt to be repaid was made by man. But man, by his nature is finite and thus incapable of making infinite reparation.
And so God the Father, sent his only Son, Jesus Christ, who is infinite, to become man, and as man, offer infinite reparation to God by dying on the cross. And so Jesus did. All this, so that humanity would once again be united in friendship with God.
But that's not the end of the story...
The gift of free will still remains. It is the gift of choice. It is the gift that allows us, if we so choose, to love God and prove our love by obedience.
Ref: The Faith Explained by Leo J. Trese